CVE-2026-38641: relibc Denial of Service Vulnerability in mmap_and_copy

Technical summary

The vulnerability exists in the DSO::mmap_and_copy function within relibc commit 61f42d. This function is responsible for memory-mapping and copying operations during shared library loading. A crafted shared library can trigger improper error handling or resource management in this function, causing an uncontrolled crash. The issue stems from insufficient validation or bounds-checking when processing library data, classified under CWE-404 (Improper Resource Validation).

Business impact

Services relying on relibc for dynamic library loading face availability risk. An unauthenticated remote attacker can disrupt operations without credentials or user action, leading to service downtime. This is particularly concerning for long-running daemons, containerized applications, or microservices that dynamically load libraries at runtime. Recovery requires manual intervention or automated restart mechanisms.

Affected systems

Any application or system built with or embedding relibc is potentially affected. Since relibc is a Rust standard library alternative used in certain embedded and systems programming contexts, impact is concentrated in projects explicitly adopting relibc. The lack of vendor or product metadata in the disclosure suggests this affects a narrower ecosystem than mainstream C/C++ runtimes; however, you should audit your supply chain for relibc dependencies.

Exploitability

Exploitability is high. The attack vector is network-based, requires no authentication or privileges, and demands no user interaction. An attacker need only cause an affected application to load a crafted shared library—this could occur through supply chain compromise (trojanized library), local file placement, or if the application dynamically loads libraries from attacker-controlled or insufficiently validated sources. The low complexity score reflects the straightforward nature of the attack.

Remediation

Update relibc to a patched commit beyond 61f42d. Verify the exact patched version against the relibc project's security advisories and release notes. Additionally, implement network segmentation to restrict which sources can deliver shared libraries to your applications, and use code signing or integrity verification for all dynamically loaded libraries.

Patch guidance

Monitor the relibc project repository and official security channels for patch releases. Once available, update your build or dependency manager (e.g., Cargo for Rust projects) to reference the fixed commit or release version. Test patches in a staging environment before production rollout. If you maintain custom builds of relibc, review the changes in commit 61f42d and apply the necessary fixes from upstream.

Detection guidance

Monitor for unexpected process crashes or restarts in applications using relibc, especially if correlated with new or modified shared library files in your environment. Log dynamic library loading attempts and their sources. Use host-based intrusion detection to flag attempts to load suspicious or unsigned libraries. In containerized environments, scan images for relibc and vulnerable commits during CI/CD.

Why prioritize this

This vulnerability merits prompt attention due to its high CVSS score (7.5), unauthenticated network exploitability, and denial-of-service impact. Although not yet in CISA's Known Exploited Vulnerabilities catalog, the low barrier to exploitation and availability impact justify rapid patching. Prioritize systems where relibc is a critical dependency and where downtime carries business cost.

Risk score, explained

The CVSS 3.1 score of 7.5 (HIGH) reflects the combination of network accessibility (AV:N), low attack complexity (AC:L), no authentication requirement (PR:N), no user interaction (UI:N), and high availability impact (A:H). The vulnerability does not affect confidentiality or integrity, which caps the severity below critical. The overall rating appropriately captures a serious but containable risk.

Frequently asked questions