CVE-2026-17556: GitHub Enterprise Server path traversal (CVSS 9.1)

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.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityNone

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Affected products

GitHub Enterprise Server≥ 3.18.0 < 3.18.13 · ≥ 3.19.0 < 3.19.10 · ≥ 3.20.0 < 3.20.6 · ≥ 3.21.0 < 3.21.4

Remediation

Fixed in

GitHub Enterprise Server≥ 3.18.13

References

https://docs.github.com/en/[email protected]/admin/release-notes#3.17.19ProductRelease Notes
https://docs.github.com/en/[email protected]/admin/release-notes#3.18.13ProductRelease Notes
https://docs.github.com/en/[email protected]/admin/release-notes#3.19.10ProductRelease Notes
https://docs.github.com/en/[email protected]/admin/release-notes#3.20.6ProductRelease Notes
https://docs.github.com/en/[email protected]/admin/release-notes#3.21.4ProductRelease Notes

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-17556 being actively exploited?

CVE-2026-17556 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.80%.

How severe is CVE-2026-17556?

CVE-2026-17556 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.80% probability of exploitation.

Which products are affected by CVE-2026-17556?

Affected products include GitHub Enterprise Server.

How do I fix CVE-2026-17556?

Upgrade affected software to a fixed version, for example GitHub Enterprise Server 3.18.13 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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