CVE-2026-17556: Path traversal in GitHub Enterprise Server allowed unauthenticated deletion of instance storage via the X-GitHub-Request-Id header

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-05 · updated 2026-10-23
Weakness: CWE-22

Description

A path traversal vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated attacker to delete arbitrary files and directories on the instance, including the entire user storage directory containing Git LFS objects, release assets, attachments, and avatars. The X-GitHub-Request-Id request header was used without sanitization as a filesystem path segment for the upload buffer directory, so a traversal value pointed the buffer at an arbitrary path and the deferred cleanup routine recursively removed the traversed target. Exploitation required only network reachability to the instance and no authentication, and it worked even when private mode was enabled. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.22 and was fixed in versions 3.21.4, 3.20.6, 3.19.10, 3.18.13 and 3.17.19. This vulnerability was reported via the GitHub Bug Bounty program.

Affected products

GitHub Enterprise Server: before 3.17.19; from 3.18.0 before 3.18.13; from 3.19.0 before 3.19.10; from 3.20.0 before 3.20.6; from 3.21.0 before 3.21.4 — fixed in 3.17.19, 3.18.13, 3.19.10, 3.20.6, 3.21.4

How to fix

Upgrade to a fixed version: GitHub Enterprise Server 3.17.19, 3.18.13, 3.19.10, 3.20.6. Check the vendor advisory for mitigations.

References

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