CVE-2026-26247: Code.gitea.io/gitea Gitea OAuth2 PKCE S256 Verifier Vulnerability

CRITICAL
Advisory Identifier: GHSA-m5ch-ppfx-xv3v
Share
CVSS 9.1
CWE-284
Published
Advisory Summary

CVE-2026-26247 is a CRITICAL (CVSS 9.1) gitea oauth2 pkce s256 verifier vulnerability (CWE-284: Improper Access Control) affecting Code.gitea.io/gitea libraries in the Go ecosystem. The issue involves gitea oauth2 pkce s256 verifier bypass. Remediation is available by upgrading affected packages to version 1.25.5.

CVE-2026-26247 at a Glance

CVE Identifier CVE-2026-26247
GHSA Identifier GHSA-m5ch-ppfx-xv3v
Severity CRITICAL
CVSS v3.1 Base Score 9.1
CWE Classification CWE-284: Improper Access Control
Affected Product Code.gitea.io/gitea
Package Ecosystem Go
Published Date
Last Updated

Security Impact

CVSS: 9.1

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-26247

To remediate this vulnerability, upgrade all affected Code.gitea.io/gitea dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

code.gitea.io/gitea fixed: 1.25.5 
Upgrade code.gitea.io/gitea to 1.25.5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for code.gitea.io/gitea

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-26247, inspect your project dependencies for Code.gitea.io/gitea:

inspect dependencies for code.gitea.io/gitea

Analyze the terminal output to locate any version of Code.gitea.io/gitea in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.25.5), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-284: Improper Access Control, where the product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. In Code.gitea.io/gitea, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Gitea versions before 1.25.5 do not persist the OAuth2 PKCE S256 challenge method correctly during authorization, allowing token exchange without the expected verifier check.

CVE-2026-26247 Affected Code.gitea.io/gitea Versions

1 component(s)
Fixed Versions:
1.25.5
Product / Package Ecosystem Affected Versions Fixed Version
code.gitea.io/gitea
golang/code.gitea.io/gitea
Go
< 1.25.5
1.25.5

References

NVD — CVE-2026-26247 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-26247
Code.gitea.io/gitea Source Repository REPOSITORY
https://github.com/go-gitea/gitea/pull/36462
Code.gitea.io/gitea Source Repository REPOSITORY
https://github.com/go-gitea/gitea/pull/36477
Security Fix Commit FIX COMMIT
https://github.com/go-gitea/gitea/commit/750649c1ef092c95f95b206b9d5fa17471a0b1f5
Security Fix Commit FIX COMMIT
https://github.com/go-gitea/gitea/commit/bf8d11bb212ba2a76596d8a90e74e7d664571324
blog.gitea.com/release-of-1.25.5 WEB
https://blog.gitea.com/release-of-1.25.5
Code.gitea.io/gitea Source Repository REPOSITORY
https://github.com/go-gitea/gitea
Code.gitea.io/gitea Release RELEASE
https://github.com/go-gitea/gitea/releases/tag/v1.25.5

Frequently Asked Questions

What is CVE-2026-26247?
CVE-2026-26247 is a security vulnerability in Code.gitea.io/gitea involving Gitea OAuth2 PKCE S256 verifier bypass under CWE-284: Improper Access Control.
Which Code.gitea.io/gitea versions are affected?
Affected versions include releases prior to 1.25.5 across affected packages: code.gitea.io/gitea.
What version fixes CVE-2026-26247?
Upgrading to 1.25.5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is code.gitea.io/gitea affected?
Yes, code.gitea.io/gitea is affected in releases prior to 1.25.5. Upgrade your dependency to 1.25.5 or later.
What is the CVSS score of CVE-2026-26247?
CVE-2026-26247 has a CVSS v3.1 base score of 9.1 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
What CWE is associated with CVE-2026-26247?
CVE-2026-26247 is classified under CWE-284: Improper Access Control (The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.).
How can I check Go dependencies for CVE-2026-26247?
Run the dependency tree command: 'inspect dependencies for code.gitea.io/gitea'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-m5ch-ppfx-xv3v",
  "modified" : "2026-09-01T17:23:03Z",
  "published" : "2026-07-03T21:31:37Z",
  "aliases" : [ "CVE-2026-26247" ],
  "summary" : "Gitea OAuth2 PKCE S256 verifier bypass",
  "details" : "Gitea versions before 1.25.5 do not persist the OAuth2 PKCE S256 challenge method correctly during authorization, allowing token exchange without the expected verifier check.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "code.gitea.io/gitea"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.25.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-26247"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/pull/36462"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/pull/36477"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/commit/750649c1ef092c95f95b206b9d5fa17471a0b1f5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/commit/bf8d11bb212ba2a76596d8a90e74e7d664571324"
  }, {
    "type" : "WEB",
    "url" : "https://blog.gitea.com/release-of-1.25.5"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/go-gitea/gitea"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/go-gitea/gitea/releases/tag/v1.25.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-284" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-01T17:23:03Z",
    "nvd_published_at" : "2026-07-03T21:16:58Z"
  }
}