Alexey Vishnyakov



I completed bachelor’s and master’s degrees in the Faculty of Computational Mathematics and Cybernetics at Lomonosov Moscow State University. I received PhD at Ivannikov Institute for System Programming of the RAS.

I work as a Senior DevSecOps Engineer at Yandex Cloud.

I have a strong interest in computer security, security development lifecycle (SDL), symbolic execution, fuzzing, automatic bug detection, return-oriented programming, dynamic analysis, binary analysis, compilers, and developing tools for all the above.


Publications and Talks


Numeric Truncation Security Predicate [paper] [slides] [russian video]

Mezhuev T., Kobrin I., Vishnyakov A., Kuts D. Numeric Truncation Security Predicate. 2023 Ivannikov ISPRAS Open Conference (ISPRAS), IEEE, 2023, p. 84-92. DOI: 10.1109/ISPRAS60948.2023.10508174


Numeric truncation is a widely spread error in software written in languages with static data typing, such as C/C++ or Java. It occurs when the significant bits of the value with a bigger type size are truncated during value conversion to the smaller type. Utilizing one of the most powerful methods for path exploration and automated bug detection called dynamic symbolic execution (DSE), we propose the symbolic security predicate for numeric truncation error detection, developed on top of DSE tool Sydr. Firstly, we execute the program on the data, which does not lead to any errors. During program execution we update symbolic shadow stack and shadow registers to track symbolic sizes of the symbolic variables to avoid false positives. Then, if we meet the instruction, which truncates the symbolic variable, we build the security predicate, try to solve it with the SMT-solver and in case of success save new input file to reproduce the error. We tested our approach on Juliet Dynamic test suite for CWE-197 and achieved 100% accuracy. We approved the workability of our approach by detecting 12 new errors of numeric truncation in 5 different real-world open source projects within OSS-Sydr-Fuzz project. All of the errors were reported, most of the reports were equipped with appropriate fixes, successfully confirmed and applied by project maintainers.

Fuzzing for SDL: Select, Cover, Reveal [slides] [russian video]

Vartan Padaryan, Vlad Stepanov, Alexey Vishnyakov. Fuzzing for SDL: Select, Cover, Reveal. OFFZONE 2023.


Fuzz testing is one of the basic techniques used in secure software development. To reap its benefits, developers must deeply integrate fuzz testing into software development processes and establish links with attack surface analysis, functional testing, sanitizers, automated parsing of detected failures.

The talk covers both the fuzz engine and the process of selecting fuzz targets. Dynamic taint analysis coupled with virtual machine introspection allows you to find interfaces of complex software, through which an intruder will attack your software in the first place, and prioritize the fuzz order in resource-constrained environments. And hybrid fuzz testing with dynamic symbolic execution helps you quickly achieve good code coverage and detect errors even if they do not immediately lead to visible software failures

CASR: Your Life Vest in a Sea of Crashes [slides] [russian video]

Andrey Fedotov, Alexey Vishnyakov. CASR: Your Life Vest in a Sea of Crashes. OFFZONE 2023.


CASR is an open‑source crash triage framework designed to handle post‑fuzzing challenges in security research and software development. It enables crash report generation, deduplication, clustering, and severity estimation while being integrated with modern fuzzers like AFL++, LibAFL, and libFuzzer.

CASR supports multiple architectures (x86, ARM, RISC‑V), programming languages (C/C++/Go/Rust/Python/Java) and includes LibCASR for the development of custom analysis tools. It also offers casr‑dojo for exporting crashes to DefectDojo. CASR is a valuable tool for security researchers and developers dealing with fuzzing and vulnerability management.

The CASR tool set implements the following fuzzing crash triage pipeline: crash report creation with all necessary information for manual analysis, significant reduction of duplicate crashes, clustering, creating UBSAN reports, and uploading new reports to the DefectDojo vulnerability management system

Sydr-Fuzz: Continuous Hybrid Fuzzing and Dynamic Analysis for Security Development Lifecycle [paper] [slides] [russian video]

Vishnyakov A., Kuts D., Logunova V., Parygina D., Kobrin E., Savidov G., Fedotov A. Sydr-Fuzz: Continuous Hybrid Fuzzing and Dynamic Analysis for Security Development Lifecycle. 2022 Ivannikov ISPRAS Open Conference (ISPRAS), IEEE, 2022, pp. 111-123. DOI: 10.1109/ISPRAS57371.2022.10076861


Nowadays automated dynamic analysis frameworks for continuous testing are in high demand to ensure software safety and satisfy the security development lifecycle (SDL) requirements. The security bug hunting efficiency of cutting-edge hybrid fuzzing techniques outperforms widely utilized coverage-guided fuzzing. We propose an enhanced dynamic analysis pipeline to leverage productivity of automated bug detection based on hybrid fuzzing. We implement the proposed pipeline in the continuous fuzzing toolset Sydr-Fuzz which is powered by hybrid fuzzing orchestrator, integrating our DSE tool Sydr with libFuzzer and AFL++. Sydr-Fuzz also incorporates security predicate checkers, crash triaging tool Casr, and utilities for corpus minimization and coverage gathering. The benchmarking of our hybrid fuzzer against alternative state-of-the-art solutions demonstrates its superiority over coverage-guided fuzzers while remaining on the same level with advanced hybrid fuzzers. Furthermore, we approve the relevance of our approach by discovering 85 new real-world software flaws within the OSS-Sydr-Fuzz project. Finally, we open Casr source code to the community to facilitate examination of the existing crashes.

Analyzing properties of path predicate slicing algorithm [russian paper]

Vishnyakov A.V. Analyzing properties of path predicate slicing algorithm. Proceedings of the Institute for System Programming of the RAS. ISP RAS, vol. 34, issue 3, 2022. pp. 7-12 (in Russian). DOI: 10.15514/ISPRAS-2022-34(3)-1


Security development lifecycle (SDL) is applied to improve software reliability and security. It extends program lifecycle with additional testing of security properties. Among other things, fuzz testing is widely used, which allows one to detect crashes and hangs of the analyzed code. The hybrid approach that combines fuzzing and dynamic symbolic execution showed even greater efficiency than classical fuzzing. Moreover, symbolic execution empowers one to add additional runtime checks called security predicates that detect memory errors and undefined behavior. This article explores the properties of the path predicate slicing algorithm that eliminates redundant constraints from a path predicate without accuracy loss. The article proves that the algorithm is finite and does not lose solutions. Moreover, the algorithm asymptotic complexity is estimated.

Strong Optimistic Solving for Dynamic Symbolic Execution [paper] [slides] [russian video]

Parygina D., Vishnyakov A., Fedotov A. Strong Optimistic Solving for Dynamic Symbolic Execution. 2022 Ivannikov Memorial Workshop (IVMEM), IEEE, 2022, pp. 43-53. DOI: 10.1109/IVMEM57067.2022.9983965


Dynamic symbolic execution (DSE) is an effective method for automated program testing and bug detection. It is increasing the code coverage by the complex branches exploration during hybrid fuzzing. DSE tools invert the branches along some execution path and help fuzzer examine previously unavailable program parts. DSE often faces over- and underconstraint problems. The first one leads to significant analysis complication while the second one causes inaccurate symbolic execution.

We propose strong optimistic solving method that eliminates irrelevant path predicate constraints for target branch inversion. We eliminate such symbolic constraints that the target branch is not control dependent on. Moreover, we separately handle symbolic branches that have nested control transfer instructions that pass control beyond the parent branch scope, e.g. return, goto, break, etc. We implement the proposed method in our dynamic symbolic execution tool Sydr.

We evaluate the strong optimistic strategy, the optimistic strategy that contains only the last constraint negation, and their combination. The results show that the strategies combination helps increase either the code coverage or the average number of correctly inverted branches per one minute. It is optimal to apply both strategies together in contrast with other configurations.

Error detection in binary code with dynamic symbolic execution [russian paper] [russian slides]

Vishnyakov A.V., Kobrin E.A., Fedotov A.N. Error detection in binary code with dynamic symbolic execution. Proceedings of the Institute for System Programming of the RAS. ISP RAS, vol. 34, issue 2, 2022. pp. 25-42 (in Russian). DOI: 10.15514/ISPRAS-2022-34(2)-3


Modern software is rapidly developing, revealing new program errors. More and more companies follow security development lifecycle (SDL). Fuzzing and symbolic execution are among the most popular options for supporting SDL. They allow to automatically test programs and find errors. Hybrid fuzzing is one of the most effective ways to test programs, which combines these two techniques. Checking security predicates during symbolic execution is an advanced technique, which focuses on solving extra constraints for input data to find an error and generate an input file to reproduce it. In this paper we propose a method for automatically detecting errors with the help of dynamic symbolic execution, combining hybrid fuzzing and checking security predicates. Firstly, we run hybrid fuzzing, which is required to increase number of corpora seeds. Then we minimize corpora. Thus, it would give the same coverage as the original corpora. After that we check security predicates on minimized corpora. Thus, security predicates allow to find errors like division by zero, out of bounds access, integer overflow, and more. Security predicates results are later verified with sanitizers to filter false positive results. As a result of applying the proposed method to different open source programs, we found 11 new different errors in 5 projects.

Hybrid Fuzzing of TensorFlow Machine Learning Framework [russian slides]

Kobrin E., Vishnyakov A., Fedotov A. Hybrid Fuzzing of TensorFlow Machine Learning Framework. MITSOBI 2022.

Symbolic Security Predicates: Hunt Program Weaknesses [paper] [slides] [russian video] [github]

Vishnyakov A., Logunova V., Kobrin E., Kuts D., Parygina D., Fedotov A. Symbolic Security Predicates: Hunt Program Weaknesses. 2021 Ivannikov ISPRAS Open Conference (ISPRAS), IEEE, 2021, pp. 76-85. DOI: 10.1109/ISPRAS53967.2021.00016


Dynamic symbolic execution (DSE) is a powerful method for path exploration during hybrid fuzzing and automatic bug detection. We propose security predicates to effectively detect undefined behavior and memory access violation errors. Initially, we symbolically execute program on paths that don’t trigger any errors (hybrid fuzzing may explore these paths). Then we construct a symbolic security predicate to verify some error condition. Thus, we may change the program data flow to entail null pointer dereference, division by zero, out-of-bounds access, or integer overflow weaknesses. Unlike static analysis, dynamic symbolic execution does not only report errors but also generates new input data to reproduce them. Furthermore, we introduce function semantics modeling for common C/C++ standard library functions. We aim to model the control flow inside a function with a single symbolic formula. This assists bug detection, speeds up path exploration, and overcomes overconstraints in path predicate. We implement the proposed techniques in our dynamic symbolic execution tool Sydr. Thus, we utilize powerful methods from Sydr such as path predicate slicing that eliminates irrelevant constraints.

We present Juliet Dynamic to measure dynamic bug detection tools accuracy. The testing system also verifies that generated inputs trigger sanitizers. We evaluate Sydr accuracy for 11 CWEs from Juliet test suite. Sydr shows 95.59% overall accuracy. We make Sydr evaluation artifacts publicly available to facilitate results reproducibility.

MAJORCA: Multi-Architecture JOP and ROP Chain Assembler [paper] [slides] [russian video] [github]

Nurmukhametov, A., Vishnyakov, A., Logunova V., Kurmangaleev Sh. MAJORCA: Multi-Architecture JOP and ROP Chain Assembler. 2021 Ivannikov ISPRAS Open Conference (ISPRAS), IEEE, 2021, pp. 37-46. DOI: 10.1109/ISPRAS53967.2021.00011


Nowadays, exploits often rely on a code-reuse approach. Short pieces of code called gadgets are chained together to execute some payload. Code-reuse attacks can exploit vulnerabilities in the presence of operating system protection that prohibits data memory execution. The ROP chain construction task is the code generation for the virtual machine defined by an exploited executable. It is crucial to understand how powerful ROP attacks can be. Such knowledge can be used to improve software security. We implement MAJORCA that generates ROP and JOP payloads in an architecture agnostic manner and thoroughly consider restricted symbols such as null bytes that terminate data copying via strcpy. The paper covers the whole code-reuse payloads construction pipeline: cataloging gadgets, chaining them in DAG, scheduling, linearizing to the ready-to-run payload. MAJORCA automatically generates both ROP and JOP payloads for x86 and MIPS. MAJORCA constructs payloads respecting restricted symbols both in gadget addresses and data. We evaluate MAJORCA performance and accuracy with rop-benchmark and compare it with open-source compilers. We show that MAJORCA outperforms open-source tools. We propose a ROP chaining metric and use it to estimate the probabilities of successful ROP chaining for different operating systems with MAJORCA as well as other ROP compilers to show that ROP chaining is still feasible. This metric can estimate the efficiency of OS defences.

Survey of Methods for Automated Code-Reuse Exploit Generation [paper] [github] [russian paper]

Vishnyakov, A.V. and Nurmukhametov, A.R., 2021. Survey of Methods for Automated Code-Reuse Exploit Generation. Programming and Computer Software 47(4), pp. 271-297. DOI: 10.1134/S0361768821040071


This paper provides a survey of methods and tools for automated code-reuse exploit generation. Such exploits use code that is already contained in a vulnerable program. The code-reuse approach allows one to exploit vulnerabilities in the presence of operating system protection that prohibits data memory execution. This paper contains a description of various code-reuse methods: return-to-libc attack, return-oriented programming, jump-oriented programming, and others. We define fundamental terms: gadget, gadget frame, gadget catalog. Moreover, we show that, in fact, a gadget is an instruction, and a set of gadgets defines a virtual machine. We can reduce an exploit creation problem to code generation for this virtual machine. Each particular executable file defines a virtual machine instruction set. We provide a survey of methods for gadgets searching and determining their semantics (creating a gadget catalog). These methods allow one to get the virtual machine instruction set. If a set of gadgets is Turing-complete, then a compiler can use a gadget catalog as a target architecture. However, some instructions can be absent. Hence we discuss several approaches to replace missing instructions with multiple gadgets. An exploit generation tool can chain gadgets by pattern searching (regular expressions) or considering gadgets semantics. Furthermore, some chaining methods use genetic algorithms, while others use SMT-solvers. We compare existing open-source tools and propose a testing system rop-benchmark that can be used to verify whether a generated chain successfully opens a shell.

Sydr: Cutting Edge Dynamic Symbolic Execution [paper] [video] [slides] [github] [demo]

Vishnyakov A., Fedotov A., Kuts D., Novikov A., Parygina D., Kobrin E., Logunova V., Belecky P., Kurmangaleev Sh. Sydr: Cutting Edge Dynamic Symbolic Execution. 2020 Ivannikov ISPRAS Open Conference (ISPRAS), IEEE, 2020, pp. 46-54. DOI: 10.1109/ISPRAS51486.2020.00014


The security development lifecycle (SDL) is becoming an industry standard. Dynamic symbolic execution (DSE) has enormous amount of applications in computer security (fuzzing, vulnerability discovery, reverse-engineering, etc.). We propose several performance and accuracy improvements for dynamic symbolic execution. Skipping non-symbolic instructions allows to build a path predicate 1.2–3.5 times faster. Symbolic engine simplifies formulas during symbolic execution. Path predicate slicing eliminates irrelevant conjuncts from solver queries. We handle each jump table (switch statement) as multiple branches and describe the method for symbolic execution of multi-threaded programs. The proposed solutions were implemented in Sydr tool. Sydr performs inversion of branches in path predicate. Sydr combines DynamoRIO dynamic binary instrumentation tool with Triton symbolic engine. We evaluated Sydr features on 64-bit Linux executables.

A Method for Analyzing Code-Reuse Attacks [publicly available draft] [paper] [slides] [russian paper] [russian video]

Vishnyakov, A.V., Nurmukhametov, A.R., Kurmangaleev, S.F., and Gaisaryan S.S., 2019. A Method for Analyzing Code-Reuse Attacks. Programming and Computer Software 45(8), pp. 473-484. DOI: 10.1134/S0361768819080061


Nowadays, ensuring software security is of paramount importance. Software failures can have significant consequences, and malicious vulnerability exploitation can inflict immense losses. Large corporations pay particular attention to the investigation of computer security incidents. Code-reuse attacks based on return-oriented programming (ROP) are gaining popularity each year and can bypass even modern operating system protection mechanisms. Unlike ordinary shellcode, where instructions are placed sequentially in memory, a ROP chain consists of multiple small instruction blocks (called gadgets) and uses the stack to chain them together. This makes the analysis of ROP exploits more difficult. The main goal of this work is to simplify reverse engineering of ROP exploits. A method for analyzing code-reuse attacks that allows one to split the chain into gadgets, restore the semantics of each particular gadget, and restore the prototypes and parameter values of the system calls and functions invoked during the execution of the ROP chain is proposed. The semantics of each gadget is determined by its parameterized type. Each gadget type is defined by a postcondition (Boolean predicate) that must always be true after the gadget execution. The proposed method was implemented as a software tool and tested on real-world ROP exploits found on the Internet.

Fine-Grained Address Space Layout Randomization on Program Load [paper] [slides] [russian paper] [russian slides]

Nurmukhametov, A.R., Zhabotinskiy, E.A., Kurmangaleev, S.F., Gaissaryan, S.S., and Vishnyakov, A.V., 2018. Fine-Grained Address Space Layout Randomization on Program Load. Programming and Computer Software, 44(5), pp. 363-370. DOI: 10.1134/S0361768818050080


Software vulnerabilities are a serious security threat. It is important to develop protection mechanisms preventing their exploitation, especially with a rapid increase of ROP attacks. State of the art protection mechanisms have some drawbacks that can be used by attackers. In this paper, we propose fine-grained address space layout randomization on program load that is able to protect from such kind of attacks. During the static linking stage, the executable and library files are supplemented with information about function boundaries and relocations. A system dynamic linker/loader uses this information to perform permutation of functions. The proposed method was implemented for 64-bit programs on CentOS 7 operating system. The implemented method has shown good resistance to ROP attacks evaluated by two metrics: the number of survived gadgets and the exploitability estimation of ROP chain examples. The implementation presented in this article is applicable across the entire operating system and has no compatibility problems affecting the program performance. The working capacity of proposed approach was demonstrated on real programs. The further research can cover forking randomization and finer granularity than on the function level. It also makes sense to implement the randomization of short functions placement taking into account the relationships between them. The close arrangement of functions that often call each other can improve the performance of individual programs.

Classification of ROP gadgets [russian paper] [russian slides]

Vishnyakov A.V. Classification of ROP gadgets. Trudy ISP RAN/Proc. ISP RAS, vol. 28, issue 6, 2016, pp. 27-36 (in Russian). DOI: 10.15514/ISPRAS-2016-28(6)-2


Return-oriented programming (ROP) is a dangerous exploitation technique which can be used to bypass modern defense mechanisms. ROP reuses code chunks ending with control transfer instruction from a program binary to form a chain corresponding some payload. These code chunks are called gadgets. Though, a certain set of gadgets should be available to exploit a vulnerability. Determining gadgets that can be used to form a ROP chain can be done by gadgets search and classification. This paper introduces a method for ROP gadgets classification that allows one to evaluate whether or not ROP technique can be used to exploit a program vulnerability. Classification is based on side-effects analysis of gadget execution with concrete inputs. Gadget instructions are translated into IR which is interpreted to track registers and memory usage. Initial registers and memory values are randomly generated. According to initial and final values of registers and memory gadget semantics can be explored. Classification performs several executions to determine gadget semantics. Proposed method is applied to program binaries and its capabilities were demonstrated on 32-bit and 64-bit binaries from Ubuntu 14.04. Using classification results program exploitability was confirmed for several examples. Furthermore, a possible exploitation of stack buffer overflow vulnerability in presence of write-what-where condition was shown on a model example demonstrating a bypass of canary, DEP and ASLR.

Software defect severity estimation in presence of modern defense mechanisms [russian paper]

Fedotov A.N., Padaryan V.A., Kaushan V.V., Kurmangaleev Sh.F., Vishnyakov A.V., Nurmukhametov A.R. Software defect severity estimation in presence of modern defense mechanisms. Trudy ISP RAN/Proc. ISP RAS, vol. 28, issue 5, 2016. pp. 73-92 (in Russian). DOI: 10.15514/ISPRAS-2016-28(5)-4


This paper introduces a refined method for automated exploitability evaluation of found program bugs. During security development lifecycle a significant number of crashes is detected in programs. Because of limited resources, bug fixing is time consuming and needs prioritization. It should be the matter of highest priority to fix exploitable bugs. Automated exploit generation technique is used to solve this problem in practice. Generated exploit confirms the presence of a critical vulnerability. However, state-of-the-art publications omit modern defense mechanisms preventing exploitation. It results in lowering of an evaluation quality. This paper considers modern vulnerability exploitation prevention mechanisms. An evaluation of their prevalence and efficiency is also presented. The method can be applied to program binaries and doesn’t require any debug information. Proposed method is based on symbolic interpretation of traces obtained by a full-system emulator. Our method can demonstrate a real exploitability for stack buffer overflow vulnerability with write-what-where condition even when DEP, ASLR, and “canary” operate together. The implemented method capabilities were shown on model examples and real programs.