GitHub Enterprise Server <3.21 OAuth Redirect URI Regex Bypass
CVE-2026-4296 Published on April 21, 2026
Incorrect Regular Expression vulnerability in GitHub Enterprise Server allowed unauthorized access to user accounts via OAuth callback URL validation bypass
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.
Vulnerability Analysis
CVE-2026-4296 is exploitable with network access. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
Incorrect Regular Expression
The software specifies a regular expression in a way that causes data to be improperly matched or compared. When the regular expression is used in protection mechanisms such as filtering or validation, this may allow an attacker to bypass the intended restrictions on the incoming data.
Products Associated with CVE-2026-4296
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Affected Versions
GitHub Enterprise Server:- Version 3.14.0, <= 3.14.25 is affected.
- Version 3.15.0, <= 3.15.20 is affected.
- Version 3.16.0, <= 3.16.16 is affected.
- Version 3.17.0, <= 3.17.13 is affected.
- Version 3.18.0, <= 3.18.7 is affected.
- Version 3.19.0, <= 3.19.4 is affected.
- Version 3.20.0 and below 3.20.1 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.