CVE-2026-4296: GitHub Enterprise Server vulnerability (CVSS 8.8)

Description

An incorrect regular expression vulnerability was identified in GitHub Enterprise Server that allowed an attacker to bypass OAuth redirect URI validation. An attacker with knowledge of a first-party OAuth application's registered callback URL could craft a malicious authorization link that, when clicked by a victim, would redirect the OAuth authorization code to an attacker-controlled domain. This could allow the attacker to gain unauthorized access to the victim's account with the scopes granted to the OAuth application. This vulnerability affected all versions of GitHub Enterprise Server prior to 3.21 and was fixed in versions 3.20.1, 3.19.5, 3.18.8, 3.17.14, 3.16.17, 3.15.21, 3.14.26. This vulnerability was reported via the GitHub Bug Bounty program.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionRequired

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Affected products

GitHub Enterprise Server≥ 3.15.0 < 3.15.21 · ≥ 3.16.0 < 3.16.17 · ≥ 3.17.0 < 3.17.14 · ≥ 3.18.0 < 3.18.8

Remediation

Fixed in

GitHub Enterprise Server≥ 3.15.21

Patch & vendor advisories

References

https://docs.github.com/en/[email protected]/admin/release-notes#3.14.26Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.15.21Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.16.17Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.17.14Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.18.8Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.19.5Release NotesVendor Advisory
https://docs.github.com/en/[email protected]/admin/release-notes#3.20.1Release NotesVendor Advisory

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-4296 being actively exploited?

CVE-2026-4296 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.74%.

How severe is CVE-2026-4296?

CVE-2026-4296 has a CVSS 3.1 base score of 8.8, rated high. EPSS estimates a 0.74% probability of exploitation.

Which products are affected by CVE-2026-4296?

Affected products include GitHub Enterprise Server.

How do I fix CVE-2026-4296?

Upgrade affected software to a fixed version, for example GitHub Enterprise Server 3.15.21 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-4296 against the real software inventory on every managed device, as each hourly inventory arrives. 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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