CVE-2026-95818 in glibc
Summary
by MITRE • 09/22/2026
A stack-based buffer overflow in the dynamic loader (ld.so) of the GNU C Library (glibc) versions 2.14 through 2.44 allows a local attacker to crash or corrupt the memory of setuid/setgid (AT_SECURE) programs.
When such a program's DT_RPATH or DT_RUNPATH begins with $ORIGIN and is followed by NUL or '/' the loader both reads past the end of the path buffer and writes past the end of a stack-allocated internal buffer. The corrupted loader stack can lead to a loader crash (denial of service) and limited disclosure of process memory.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified in this context represents a critical security flaw within the dynamic linker, ld.so, which is an integral component of the GNU C Library (glibc). This issue affects glibc versions ranging from 2.14 through 2.44 and specifically targets setuid or setgid programs that operate under elevated privileges, indicated by the AT_SECURE flag in their environment. The root cause lies in improper boundary checking during the processing of library search paths defined via DT_RPATH or DT_RUNPATH ELF program headers. When these path strings begin with the $ORIGIN token followed immediately by a NUL byte or a forward slash character, the dynamic loader fails to correctly validate buffer lengths before performing memory operations. This logic error results in out-of-bounds reads and writes that extend beyond the allocated stack-allocated internal buffers used for resolving library paths during program initialization.
From a technical perspective, this flaw is classified as a stack-based buffer overflow, which aligns with CWE-121: Stack-based Buffer Overflow. The vulnerability exploits the way glibc handles variable-length path expansions in privileged contexts. Normally, setuid programs undergo strict security checks to prevent privilege escalation attacks by restricting environment variables and library loading mechanisms. However, the specific condition involving $ORIGIN combined with a NUL or slash character bypasses these safeguards due to an off-by-one error or similar boundary miscalculation within the loader's string handling routines. As the dynamic linker processes the path, it reads past the end of the designated path buffer and subsequently writes beyond the limits of its internal stack buffer. This corruption overwrites adjacent memory locations on the call stack, potentially altering return addresses, saved frame pointers, or other critical control data structures maintained by the loader itself rather than the target application directly.
The operational impact of this vulnerability is severe for systems relying on glibc for dynamic linking in privileged applications. The immediate consequence is a denial of service condition caused by a crash within the dynamic linker process. Since ld.so operates before the main program logic begins, its failure prevents the setuid or setgid binary from executing entirely, leading to application instability and potential service disruption. Beyond availability issues, the vulnerability poses significant risks related to confidentiality due to limited disclosure of process memory. The out-of-bounds read operation can leak sensitive data stored in adjacent stack frames, such as environment variables, command-line arguments, or other confidential information belonging to the privileged process. While direct remote code execution is not explicitly confirmed for all scenarios, the ability to corrupt loader state and disclose memory contents provides a foothold that could potentially be leveraged by local attackers to further compromise system integrity or escalate privileges depending on the specific runtime environment and mitigations in place.
This vulnerability maps closely to ATT&CK technique T1059: Command and Scripting Interpreter, specifically regarding the abuse of legitimate system utilities for malicious purposes, although it is more accurately categorized under initial access vectors involving local privilege escalation attempts via binary exploitation techniques like CWE-787 or CWE-122. The attack vector requires local physical or network-accessible shell access to a user account that can execute setuid binaries with the specific DT_RPATH or DT_RUNPATH configuration, making it primarily a local threat rather than a remote one. Attackers must craft an ELF binary with carefully constructed dynamic section headers to trigger the overflow condition during execution.
Mitigation strategies for this vulnerability prioritize upgrading glibc to versions beyond 2.44 where the boundary checks have been corrected and hardened against such path manipulation attacks. For systems that cannot immediately upgrade, administrators should audit setuid/setgid binaries for custom DT_RPATH or DT_RUNPATH settings that utilize $ORIGIN expansions followed by NUL bytes or slashes. Removing unnecessary library search paths from privileged executables reduces the attack surface significantly. Additionally enabling stack protector mechanisms and Address Space Layout Randomization (ASLR) can mitigate exploitation attempts by making memory corruption harder to predict, although these are compensating controls rather than definitive fixes for the underlying logic error in glibc itself. Regular patch management and monitoring of system logs for abnormal process terminations related to ld.so crashes are recommended operational practices to detect potential exploitation attempts or stability issues arising from this flaw.