Enterprise Server: Improper Limitation of a Pathname to a Restricted Directory
CVE-2026-17556 is a critical-severity improper limitation of a pathname to a restricted directory vulnerability in Enterprise Server from GitHub, with a CVSS 3.1 base score of 9.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Enterprise Server versions: 3.17.0 through 3.17.18; 3.18.0 through 3.18.12; 3.19.0 through 3.19.9, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.8% chance of exploitation within 30 days, higher than 57% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of Enterprise Server you run against the affected versions below, and install the vendor's latest release.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| GitHub | Enterprise Server | 3.17.0 through 3.17.18; 3.18.0 through 3.18.12; 3.19.0 through 3.19.9; 3.20.0 through 3.20.5; 3.21.0 through 3.21.3 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.8 | High | CNA (github.com) |
| CVSS 3.1 | 9.1 | Critical | NVD |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Limitation of a Pathname to a Restricted Directory
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
How developers prevent this class of flaw
- For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.
More Improper Limitation of a Pathname to a Restricted Directory vulnerabilities (CWE-22)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- docs.github.com/en/[email protected]/admin/release-notes#3.17.19Product, Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.18.13Product, Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.19.10Product, Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.20.6Product, Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.21.4Product, Release Notes
Other vulnerabilities in Enterprise Server
- 7.7 High severity
- 8.8 High severity
- 9.8 Critical severity
- 8.8 High severity
- 7.5 High severity
- 7.4 High severity
Recent Improper Limitation of a Pathname to a Restricted Directory vulnerabilities
- 8.6 High severity
- 8.8 High severity
- 7.7 High severity
- 9.3 Critical severity
- 8.1 High severity
- 8.0 High severity
Spotted an error? Tell us.