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CVE-2026-8606: Server-Side Request Forgery in GitHub Enterprise Server via Advisory Package URL Endpoint

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-27 · updated 2026-07-23
• Weakness: CWE-918

Description

A Server-Side Request Forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an attacker to cause the server to issue HTTP requests to internal services via the security advisories package lookup feature. By directing requests to an internal management service and measuring response timing, an attacker could infer the values of sensitive environment variables, including signing secrets and private keys. Exploitation required GitHub Packages to be enabled; on instances not running in private mode the vulnerability was exploitable without authentication, otherwise any authenticated user could exploit it. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21.1 and was fixed in versions 3.20.3, 3.19.7, 3.18.10, 3.17.16, and 3.16.19. This vulnerability was reported via the GitHub Bug Bounty program.

Affected products

• GitHub Enterprise Server: before 3.16.19; from 3.17.0 before 3.17.16; from 3.18.0 before 3.18.10; from 3.19.0 before 3.19.7; from 3.20.0 before 3.20.3; 3.21.0 — fixed in 3.16.19, 3.17.16, 3.18.10, 3.19.7, 3.20.3

How to fix

Upgrade to a fixed version: GitHub Enterprise Server 3.16.19, 3.17.16, 3.18.10, 3.19.7. Check the vendor advisory for mitigations.

References

• https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.19
• https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.16
• https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.10
• https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.7
• https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.3
• https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.1

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