# CVE-2026-56657: Gitea SSH key parser denial of service in normalization loop

Source: https://junglewise.ai/threats/cve-2026-56657-gitea-ssh-key-parser-denial-of-service-in-normalization-loop  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-21. Updated: 2026-07-21  
License: CC BY 4.0 with a link back

CVE-2026-56657 · Severity: medium · CVSS 3.1 · Published 2026-07-21

Gitea is an open-source forge software package for hosting software development version control using Git. A vulnerability in how the system processes SSH keys allows an authenticated user to crash the server by uploading a specially crafted, large key file. This can lead to a total service outage, preventing teams from accessing their code repositories and disrupting development operations.

Technologies: [Gitea](https://junglewise.ai/threats/technologies/gitea), [code.gitea.io/gitea (Go)](https://junglewise.ai/threats/technologies/code-gitea-io-gitea), [gitea.dev (Go)](https://junglewise.ai/threats/technologies/gitea-dev). Vendors: [Gitea](https://junglewise.ai/threats/vendors/gitea), [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-56657 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56657 being exploited in the wild.

**How severe is CVE-2026-56657?** Medium severity, with a CVSS score of 3.1, published 21 July 2026.

**Which products and versions are affected?** Gitea < 1.27.0; code.gitea.io/gitea (Go) < 1.27.0, SEMVER:introduced=0,fixed=1.27.0; gitea.dev (Go) SEMVER:introduced=0,fixed=1.27.0.

**Is there a fix for CVE-2026-56657?** Yes. code.gitea.io/gitea (Go): upgrade to 1.27.0 or later; gitea.dev (Go): upgrade to 1.27.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56657 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-56657?** Check whether you run Gitea, code.gitea.io/gitea (Go) or gitea.dev (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- code.gitea.io/gitea (Go): upgrade to 1.27.0 or later

  ```sh
  go get code.gitea.io/gitea@v1.27.0
  ```

- gitea.dev (Go): upgrade to 1.27.0 or later

  ```sh
  go get gitea.dev@v1.27.0
  ```


## Technical details

The vulnerability exists in the `parseKeyString` function within Gitea's SSH key normalization logic. When processing RFC 4716 (SSH2) format keys, the application splits the input on newlines and accumulates the key body using the `+=` operator in Go. Because Go strings are immutable, this results in an O(N²) complexity for both time and memory allocations as the entire string is copied for every line processed. An authenticated attacker can submit a key with hundreds of thousands of short lines to trigger quadratic resource consumption before any size validation or cryptographic checks occur. This leads to rapid CPU exhaustion and Out-of-Memory (OOM) conditions. The issue is fixed in version 1.27.0.

## Affected products

- Gitea Gitea < 1.27.0

## Identifiers

- CVE-2026-56657
- GHSA-4xjf-493q-98p3
- GO-2026-6042

## Timeline

- 2026-07-13: disclosed: Initial disclosure on GitHub Advisory Database
- 2026-07-21: advisory: Advisory updated and published

## References

- [https://api.github.com/users/AdamKorcz](https://api.github.com/users/AdamKorcz)
- [https://github.com/AdamKorcz](https://github.com/AdamKorcz)
- [https://api.github.com/users/AdamKorcz/gists%7B/gist_id%7D](https://api.github.com/users/AdamKorcz/gists%7B/gist_id%7D)
- [https://api.github.com/users/AdamKorcz/repos](https://api.github.com/users/AdamKorcz/repos)
- [https://avatars.githubusercontent.com/u/44787359?v=4](https://avatars.githubusercontent.com/u/44787359?v=4)
- [https://api.github.com/users/AdamKorcz/events%7B/privacy%7D](https://api.github.com/users/AdamKorcz/events%7B/privacy%7D)

## Related threats

- [Gitea account takeover via OAuth2 auto-linking](https://junglewise.ai/threats/cve-2026-120263-when-oauth2-client-account-linking-is-set-to-auto-not-the)
- [Gitea limited-visibility profile disclosure via public-only token](https://junglewise.ai/threats/cve-2026-119627-the-web-profile-and-rss-atom-feed-routes-of-users-and)
- [Gitea token scope bypass in web routes](https://junglewise.ai/threats/cve-2026-119625-the-username-web-route-accepted-personal-access-tokens-over-http)
- [Gitea project boards information disclosure of private pull requests](https://junglewise.ai/threats/cve-2026-119533-repository-and-organization-project-boards-listed-the-pull)
- [Gitea API token scope bypass in repository deletion](https://junglewise.ai/threats/cve-2026-119441-delete-api-v1-orgs-org-repos-deletes-all-repositories-of-an)