CVE-2026-5958: Race Condition in GNU Sed

Vulnerability summary

CVE-2026-5958 is a low (CVSS 2.1) vulnerability in gnu sed. EPSS estimates a 0.14% chance of exploitation in the next 30 days, higher than 2.8% of scored vulnerabilities.

Timeline

1. 20-04-2026
   PublishedVulnerability first disclosed.
2. 13-05-2026
   Last modifiedVulnerability information updated.

Description

When sed is invoked with both -i (in-place edit) and --follow-symlinks, the function open_next_file() performs two separate, non-atomic filesystem operations on the same path: 1. resolves symlink to its target and stores the resolved path for determining when output is written, 2. opens the original symlink path (not the resolved one) to read the file. Between these two calls there is a race window. If an attacker atomically replaces the symlink with a different target during that window, sed will: read content from the new (attacker-chosen) symlink target and write the processed result to the path recorded in step 1. This can lead to arbitrary file overwrite with attacker-controlled content in the context of the sed process. This issue was fixed in version 4.10.

• CWE-367Time-of-check Time-of-use (TOCTOU) Race ConditionThe product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.