CVE-2021-33463 in yasm
Summary
by MITRE • 07/26/2022
An issue was discovered in yasm version 1.3.0. There is a NULL pointer dereference in yasm_expr__copy_except() in libyasm/expr.c.
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Analysis
by VulDB Data Team • 07/26/2022
The vulnerability identified as CVE-2021-33463 represents a critical NULL pointer dereference flaw within the yasm assembler version 1.3.0. This issue resides in the yasm_expr__copy_except() function located in the libyasm/expr.c source file, which forms part of the core expression handling mechanisms within the yasm assembly framework. The vulnerability manifests when the software attempts to dereference a null pointer during expression copying operations, creating a potential crash condition that can be exploited by malicious actors.
The technical nature of this flaw places it within the realm of software reliability and memory safety issues, specifically categorized under CWE-476 which defines NULL Pointer Dereference. This vulnerability occurs during the processing of assembly expressions where the yasm tool attempts to copy expression structures while failing to properly validate pointer references. The flaw is particularly concerning because it can be triggered through malformed input files or crafted assembly code that causes the expression copying routine to access uninitialized or null memory references. The function yasm_expr__copy_except() appears to lack proper null checks before dereferencing pointers, leading to an immediate system crash or potential exploitation for more advanced attack vectors.
From an operational impact perspective, this vulnerability affects any system utilizing yasm version 1.3.0 for assembly processing, including development environments, build systems, and automated assembly toolchains. The NULL pointer dereference can cause denial of service conditions where legitimate assembly operations fail, potentially disrupting development workflows and build processes. In certain scenarios, this flaw could be leveraged as part of a broader attack chain, particularly in environments where yasm is used to process untrusted assembly input or when integrated into larger software supply chain components. The vulnerability's impact extends beyond simple crashes as it represents a potential entry point for more sophisticated exploitation techniques.
Security practitioners should consider this vulnerability in the context of the ATT&CK framework, specifically under the T1203 - Exploitation for Client Execution and T1499 - Endpoint Denial of Service tactics. The vulnerability can be exploited to cause system instability and service disruption, making it particularly dangerous in automated build environments or continuous integration pipelines where yasm is frequently invoked. Mitigation strategies should include immediate patching to version 1.3.1 or later, which addresses the NULL pointer dereference issue through proper validation of pointer references before dereferencing. Additionally, input validation measures should be implemented to prevent malformed assembly expressions from reaching the vulnerable code path, and system monitoring should be enhanced to detect potential exploitation attempts through crash patterns or abnormal resource consumption. Organizations should also consider implementing sandboxing mechanisms for assembly processing to isolate potential exploitation attempts and prevent escalation to more serious system compromise scenarios.