CVE-2026-38640 in relibc
Summary
by MITRE • 06/26/2026
A reachable unwrap in the __assert_fail function (/assert/mod.rs) of relibc commit 61f42d allows attackers to cause a Denial of Service (DoS) via a crafted string.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 06/26/2026
The vulnerability described represents a critical denial of service flaw within the relibc library's assertion handling mechanism. This issue manifests in the __assert_fail function located within the assert/mod.rs module of the relibc codebase. The core problem stems from an unreachable unwrap operation that occurs during assertion failure processing, creating a potential crash condition when malicious input is processed through the system's assertion framework.
The technical implementation of this vulnerability exploits a fundamental flaw in error handling where an unwrap operation is executed in a code path that should theoretically be unreachable under normal circumstances. When a crafted string is passed to the assertion mechanism, it triggers the execution of this problematic unwrap statement which leads to immediate program termination rather than graceful error handling. This behavior directly violates standard software reliability principles and creates an exploitable condition for adversaries seeking to disrupt system operations.
From an operational impact perspective, this vulnerability presents significant risk to systems relying on relibc for assertion checking and error reporting. The denial of service condition can be triggered by any malicious actor who has access to input that passes through the affected assertion mechanism, potentially leading to complete system unavailability or application crashes. The vulnerability's reachability through crafted strings indicates that it could be exploited remotely, making it particularly dangerous in networked environments where input validation is critical.
The flaw aligns with CWE-476 which categorizes null pointer dereference vulnerabilities and relates to improper error handling practices. From an attack framework perspective, this vulnerability maps to ATT&CK technique T1499.004 for network denial of service and could be leveraged as part of broader exploitation chains targeting system stability. The issue demonstrates poor defensive programming practices where developers assumed certain code paths would never execute while failing to implement proper error recovery mechanisms.
Mitigation strategies should focus on implementing robust error handling throughout the assertion framework, replacing unwrap operations with proper error propagation or fallback mechanisms. Developers should ensure that all code paths through assertion functions handle potential failure conditions gracefully without relying on unwrapping operations that can cause immediate termination. Additionally, input validation should be strengthened to prevent malicious strings from reaching the vulnerable assertion processing code, and comprehensive testing should include edge cases that might trigger the problematic code path to ensure proper handling of unexpected inputs.