CVE-2008-3196 in yacc
Summary
by MITRE
skeleton.c in yacc does not properly handle reduction of a rule with an empty right hand side, which allows context-dependent attackers to cause an out-of-bounds stack access when the yacc stack pointer points to the end of the stack.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 11/22/2017
The vulnerability described in CVE-2008-3196 resides within the yacc parser generator's skeleton.c implementation, specifically addressing how it handles grammar rules with empty right hand sides. This flaw represents a classic buffer management issue that can lead to memory corruption and potentially arbitrary code execution. The vulnerability manifests when yacc processes a grammar rule that contains an empty production, where the right hand side of the rule consists solely of an epsilon (empty) symbol, and the parser attempts to perform a reduction operation on such a rule.
The technical implementation of this vulnerability stems from improper stack pointer management within the yacc parser's internal state machine. When yacc encounters a rule with an empty right hand side, it must adjust the parser stack to account for the reduction of that rule. However, the skeleton.c implementation fails to properly validate the stack pointer bounds before performing the reduction operation. This oversight allows the parser to access memory locations beyond the allocated stack boundaries, resulting in out-of-bounds stack access. The vulnerability is context-dependent because it requires specific grammar structures and parsing conditions to be triggered, making it less straightforward to exploit than direct buffer overflow vulnerabilities.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can enable attackers to manipulate parser behavior in ways that may lead to more severe consequences. When an attacker can control the parsing of input data through a yacc-generated parser, they may be able to craft inputs that force the parser into the vulnerable code path. This could potentially allow for information disclosure through memory reads, denial of service through stack corruption, or in some cases, arbitrary code execution if the memory corruption can be carefully controlled. The vulnerability affects any application that utilizes yacc-generated parsers and processes untrusted input data, making it particularly concerning for web applications, compilers, and any software that performs grammar-based parsing of external data.
Mitigation strategies for this vulnerability require careful attention to both the immediate code fixes and broader architectural considerations. The most direct approach involves updating the yacc implementation to properly validate stack pointer bounds before performing reductions on empty rules, ensuring that the parser never attempts to access memory beyond its allocated stack space. Organizations should also implement comprehensive input validation and sanitization measures when processing data through yacc-generated parsers, particularly for applications handling untrusted input. Additionally, this vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and relates to ATT&CK techniques involving privilege escalation through memory corruption. Regular updates to parser generator tools and thorough security testing of grammar files and parsing code should be implemented as part of overall security hygiene. The vulnerability also highlights the importance of proper bounds checking in compiler and parser generator implementations, as these tools form the foundation of many applications that process structured data, making robust memory management practices essential for preventing similar issues in other components of the software stack.