CVE-2026-5921

Description

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.

Is your site exposed to CVE-2026-5921?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

8.9

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L

EPSS — Exploit Prediction

0.0007

Probability of exploitation

0.22%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-918 Server-Side Request Forgery (SSRF)

Affected Products

Vendor	Product	Versions
github	enterprise_server	< 3.14.26
github	enterprise_server	3.15.0 — 3.15.21
github	enterprise_server	3.16.0 — 3.16.17
github	enterprise_server	3.17.0 — 3.17.14
github	enterprise_server	3.18.0 — 3.18.8
github	enterprise_server	3.19.0 — 3.19.5
github	enterprise_server	All

References

Advisories & Patches

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

Frequently Asked Questions

What is CVE-2026-5921? +

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. It has a CVSS v3.1 base score of 8.9 (HIGH).

How severe is CVE-2026-5921? +

CVE-2026-5921 has a CVSS v3.1 score of 8.9 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0007, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-5921? +

CVE-2026-5921 affects products from github, specifically: enterprise_server. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-5921? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-42336

MaxKB is an open-source AI assistant for enterprise. MaxKB 2.8.0 and prior are vulnerable to a server-side request forgery (SSRF) …

CVE-2026-41682

pupnp is an SDK for development of UPnP device and control point applications. Prior to version 1.18.5, pupnp is vulnerable …

CVE-2026-44286

FastGPT is an AI Agent building platform. Prior to version 4.14.17, an unauthenticated Server-Side Request Forgery (SSRF) vulnerability allows attackers …

CVE-2026-41172

Squidex is an open source headless content management system and content management hub. Prior to version 7.23.0, an SSRF vulnerability …

CVE-2026-45412

MaxKB is an open-source AI assistant for enterprise. Prior to 2.9.1, SSRF via work_flow_template Import. Authenticated users can supply arbitrary …

CVE-2026-41129

Craft CMS is a content management system (CMS). Versions on the 4.x branch through 4.17.8 and the 5.x branch through …