CVE-2026-5921
What it is
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.
At a glance
- Exploitability
- Can be exploited over the network without logging in. High risk of data exposure, data tampering.
- Exploit odds
- 0.4% chance of exploitation in the next 30 days (EPSS).
- Fix
- A patch, advisory or fixed version is referenced. Upgrade or apply it.
Timeline
- PublishedDisclosed publicly on CVE.org and NVD
- Last updatedMost recent change to the record
Why it ranks here
- Exploited in the wild: no, CISA does not list it.
- Exploit odds: 0.4% in the next 30 days (EPSS).
- Severity: 8.9 HIGH (CVSS).
- Fix: a patch or advisory is linked.
Details
- Published
- Last modified
- Exploit probability
- 0.4% · EPSS, next 30 days
- Weakness
- CWE-918 · Server-side request forgery
- Record status
- Analyzed
Affected
- GitHub Enterprise Server < 3.14.26
- GitHub Enterprise Server < 3.15.21
- GitHub Enterprise Server < 3.16.17
- GitHub Enterprise Server < 3.17.14
- GitHub Enterprise Server < 3.18.8
- GitHub Enterprise Server < 3.19.5
- GitHub Enterprise Server 3.20.0
Attack profile CVSS 4.0 · 8.9
- Attack vector
- Network
- Complexity
- High
- Attack requirements
- Present
- Privileges needed
- None
- User interaction
- None
- Confidentiality
- High
- Integrity
- High
- Availability
- Low
Raw vector
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:H/SI:H/SA:L/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Is it in your code?
Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.
Read https://cve-list.com/agent/cve/CVE-2026-5921.md and follow it. Check whether this project is affected by CVE-2026-5921. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.
Fix and advisories
- https://docs.github.com/en/[email protected]/admin/release-notes#3.14.26
- https://docs.github.com/en/[email protected]/admin/release-notes#3.15.21
- https://docs.github.com/en/[email protected]/admin/release-notes#3.16.17
- https://docs.github.com/en/[email protected]/admin/release-notes#3.17.14
- https://docs.github.com/en/[email protected]/admin/release-notes#3.18.8
- https://docs.github.com/en/[email protected]/admin/release-notes#3.19.5
- https://docs.github.com/en/[email protected]/admin/release-notes#3.20.1
References
- https://docs.github.com/en/[email protected]/admin/release-notes#3.14.26
- https://docs.github.com/en/[email protected]/admin/release-notes#3.15.21
- https://docs.github.com/en/[email protected]/admin/release-notes#3.16.17
- https://docs.github.com/en/[email protected]/admin/release-notes#3.17.14
- https://docs.github.com/en/[email protected]/admin/release-notes#3.18.8
- https://docs.github.com/en/[email protected]/admin/release-notes#3.19.5
- https://docs.github.com/en/[email protected]/admin/release-notes#3.20.1