CVE-2026-18477 Red Hat CVE debrief

Who should care

System administrators and users with write access to directories being backed up using GNU tar should be aware of this vulnerability and take necessary precautions to mitigate the risk. This includes reviewing system backups, verifying file integrity, and monitoring for suspicious activity. Additionally, security teams and vulnerability management teams should prioritize patching and verifying the integrity of backups.

Technical summary

A Time-of-Check Time-of-Use (TOCTOU) vulnerability exists in GNU tar's incremental dumpdir 'X' rename handling. This allows a local attacker with write access to a directory being backed up to influence the restore process. During restoration, files or directories may be created, renamed, or overwritten outside the intended extraction directory, potentially leading to unauthorized file modification or privilege escalation. The vulnerability can be mitigated by updating GNU tar to the latest version and implementing compensating controls.

Defensive priority

Local attackers with write access could exploit this vulnerability to influence file restoration, potentially leading to unauthorized file modification or privilege escalation.

Recommended defensive actions

• Review and update GNU tar to the latest version
• Implement compensating controls to monitor and restrict file modifications
• Conduct regular security audits and vulnerability assessments
• Review system backups and verify file integrity
• Monitor for suspicious activity
• Track exceptions and retest remediated assets
• Close the item only after evidence is documented

Evidence notes

The CVE-2026-18477 vulnerability in GNU tar's incremental dumpdir 'X' rename handling allows local attackers with write access to influence the restore process. This could lead to unauthorized file modification or privilege escalation. Evidence is based on NVD and Red Hat sources. Further verification is needed to assess the full impact and to confirm affected systems. Defenders should review system backups, verify file integrity, and monitor for suspicious activity.

Official resources