CVE-2021-33461 in yasm
Summary
by MITRE • 07/26/2022
An issue was discovered in yasm version 1.3.0. There is a use-after-free in yasm_intnum_destroy() in libyasm/intnum.c.
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Analysis
by VulDB Data Team • 08/27/2022
The vulnerability identified as CVE-2021-33461 represents a critical use-after-free condition within the yasm assembler version 1.3.0, specifically within the yasm_intnum_destroy() function located in libyasm/intnum.c. This flaw occurs during the destruction phase of integer number objects, where memory that has already been freed is subsequently accessed or referenced, creating potential vectors for arbitrary code execution or system instability. The yasm assembler is widely utilized in software development environments for converting assembly language source code into object files, making this vulnerability particularly concerning for developers and build systems that rely on this toolchain.
The technical implementation of this use-after-free vulnerability stems from improper memory management practices within the integer number handling subsystem of yasm. When the yasm_intnum_destroy() function is invoked to release memory allocated for integer number objects, the function fails to properly invalidate references to the freed memory before the memory is deallocated. This creates a scenario where subsequent operations might attempt to access the memory location that was recently freed, leading to unpredictable behavior including crashes, data corruption, or potentially exploitable conditions. The vulnerability manifests when the assembler processes certain input files or constructs that trigger the specific code path leading to this memory management flaw, making it particularly dangerous in automated build environments or when processing untrusted input.
The operational impact of CVE-2021-33461 extends beyond simple software crashes to potentially enable remote code execution attacks. Attackers could craft malicious assembly input files that, when processed by yasm, would trigger the use-after-free condition and potentially allow for arbitrary code execution with the privileges of the user running the assembler. This vulnerability affects the broader software supply chain since yasm is commonly integrated into build systems, continuous integration pipelines, and development environments where untrusted code might be processed. The flaw is particularly dangerous in scenarios where yasm is used to process assembly code from external sources or where automated tools might invoke yasm on user-provided input, creating multiple potential attack vectors for exploitation.
Security practitioners should implement immediate mitigations including upgrading to yasm version 1.3.1 or later, which contains the necessary patches to address the memory management issue. Additionally, organizations should consider implementing input validation and sanitization measures when processing assembly code through yasm, particularly in automated environments where untrusted input might be encountered. The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software applications, and could potentially map to ATT&CK technique T1059.008 for execution through assembly language processing. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the effectiveness of potential exploitation attempts, while maintaining comprehensive monitoring for any suspicious activity related to yasm usage in their development environments.