CVE-2026-18730: Server-side request forgery vulnerability in GitHub Enterprise Server Manage API leaked a replayable gateway-agent bearer token

Severity: high (CVSS 7.4 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: 2026-09-01 · updated 2026-09-22
Weakness: CWE-918

Description

A server-side request forgery (SSRF) vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated attacker to cause the Manage API to send crafted outbound requests to an attacker-controlled host. An unauthenticated endpoint parsed an attacker-supplied cluster configuration and issued gateway-to-agent requests whose HMAC authenticated only a timestamp, not the request path or body. An attacker positioned to intercept the outbound request could capture this token and replay it against privileged management agent endpoints. High-availability deployments were not affected due to a topology restriction. This vulnerability affected GitHub Enterprise Server releases in the 3.17, 3.18, 3.19, 3.20, and 3.21 series and was fixed in versions 3.17.21, 3.18.15, 3.19.12, 3.20.8, and 3.21.6. This vulnerability was reported via the GitHub Bug Bounty program.

Affected products

GitHub Enterprise Server: before 3.17.19; from 3.18.0 before 3.18.13; from 3.19.0 before 3.19.10; from 3.20.0 before 3.20.6; from 3.21.0 before 3.21.4 — fixed in 3.17.19, 3.18.13, 3.19.10, 3.20.6, 3.21.4

How to fix

Upgrade to a fixed version: GitHub Enterprise Server 3.17.19, 3.18.13, 3.19.10, 3.20.6. Check the vendor advisory for mitigations.

References

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