CVE-2026-8034: GitHub Enterprise Server server-side request forgery (SSRF) (CVSS 9.8)

Description

A server-side request forgery (SSRF) vulnerability was identified in the GitHub Enterprise Server notebook viewer that allowed an attacker to access internal services by exploiting URL parser confusion between the validation layer and the HTTP request library. The hostname validation used a different URL parser than the request library, enabling a crafted URL to pass validation while directing the request to an unintended host. Exploitation required network access to the GitHub Enterprise Server instance. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.16.18, 3.17.15, 3.18.9, 3.19.6, and 3.20.2. This vulnerability was reported via the GitHub Bug Bounty program.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Affected products

GitHub Enterprise Server≥ 3.17.0 < 3.17.15 · ≥ 3.18.0 < 3.18.9 · ≥ 3.19.0 < 3.19.6 · ≥ 3.20.0 < 3.20.2

Remediation

Fixed in

GitHub Enterprise Server≥ 3.17.15

Patch & vendor advisories

References

https://docs.github.com/en/[email protected]/admin/release-notes#3.16.18Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.17.15Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.18.9Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.19.6Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.20.2Release NotesVendor Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-8034 being actively exploited?

CVE-2026-8034 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.86%.

How severe is CVE-2026-8034?

CVE-2026-8034 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.86% probability of exploitation.

Which products are affected by CVE-2026-8034?

Affected products include GitHub Enterprise Server.

How do I fix CVE-2026-8034?

Upgrade affected software to a fixed version, for example GitHub Enterprise Server 3.17.15 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-8034 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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