Enterprise Server: Server-Side Request Forgery
CVE-2026-5921 is a high-severity server-side request forgery vulnerability in Enterprise Server from GitHub, with a CVSS 3.1 base score of 8.9 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 3.14.26, 3.15.21, 3.16.17 as the first without the flaw, so updating Enterprise Server to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.42% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Enterprise Server to 3.14.26 or 3.15.21 or 3.16.17 or 3.17.14, whichever matches your release line, or a later version.
- Read the advisory on docs.github.com for workarounds and exact fixed builds.
- 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 | 3.14.0 up to, but not including, 3.14.26; 3.15.0 up to, but not including, 3.15.21; 3.16.0 up to, but not including, 3.16.17; 3.17.0 up to, but not including, 3.17.14; 3.18.0 up to, but not including, 3.18.8; 3.19.0 up to, but not including, 3.19.5; 3.20.0 up to, but not including, 3.20.1 | 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5 |
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
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- LowPerformance or availability is reduced.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 8.9 | High | CNA (github.com) |
| CVSS 3.1 | 8.9 | High | NVD |
Official description
A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an attacker to extract sensitive environment variables from the instance through a timing side-channel attack against the notebook rendering service. When private mode was disabled, the notebook viewer followed HTTP redirects without revalidating the destination host, enabling an unauthenticated SSRF to internal services. By chaining this with regex filter queries against an internal API and measuring response time differences, an attacker could infer secret values character by character. Exploitation required that private mode be disabled and that the attacker be able to chain the instance's open redirect endpoint through an external redirect to reach internal services. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.14.26, 3.15.21, 3.16.17, 3.17.14, 3.18.8, 3.19.5, and 3.20.1. 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: Server-Side Request Forgery
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
How developers prevent this class of flaw
- If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
- If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- docs.github.com/en/[email protected]/admin/release-notes#3.14.26Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.15.21Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.16.17Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.17.14Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.18.8Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.19.5Release Notes
- docs.github.com/en/[email protected]/admin/release-notes#3.20.1Release 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 Server-Side Request Forgery vulnerabilities
- 7.6 High severity
- 8.8 High severity
- 7.5 High severity
- 7.7 High severity
- 7.3 High severity
- 7.3 High severity
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