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GHSA-3M6Q-H5GJ-7MRW

Vulnerability from github – Published: 2026-04-22 20:37 – Updated: 2026-04-22 20:37
VLAI
Summary
Gitea has insecure default SSH settings
Details

Summary

The built-in SSH server currently advertises a number of key exchange, MAC, and host key algorithms that are considered weak or broken. The defaults should be tightened so a fresh installation passes a baseline SSH security audit out of the box.

Details

Running ssh-audit against a default deployment flags the following as fail:

  • Key exchange
  • ecdh-sha2-nistp256
  • ecdh-sha2-nistp384
  • ecdh-sha2-nistp521
  • MAC
  • hmac-sha1
  • Host key
  • ssh-rsa

Reproduction

docker run -it --rm positronsecurity/ssh-audit -p 2222 gitea.local

Impact

Default deployments expose algorithms that are known-weak or deprecated upstream. The current workaround requires manually setting several GITEA__server__SSH_SERVER_* variables, which most users will never do.

Workaround

[server]
SSH_SERVER_KEY_EXCHANGES = curve25519-sha256, diffie-hellman-group14-sha256
SSH_SERVER_CIPHERS       = chacha20-poly1305@openssh.com, aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, aes256-gcm@openssh.com
SSH_SERVER_MACS          = hmac-sha2-256-etm@openssh.com, hmac-sha2-256

There is no exposed option to restrict host key algorithms, so ssh-rsa remains advertised.

Acceptance criteria

  • [ ] Default SSH_SERVER_KEY_EXCHANGES, SSH_SERVER_CIPHERS, and SSH_SERVER_MACS updated to the secure list above.
  • [ ] New SSH_SERVER_HOST_KEY_ALGORITHMS option added, with a default that excludes ssh-rsa.
  • [ ] Documentation updated to reflect the new defaults.
  • [ ] ssh-audit against a fresh install reports no [fail] entries.
Severity
6.3 (Medium)
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "code.gitea.io/gitea"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.25.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-1188",
      "CWE-327"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-22T20:37:21Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nThe built-in SSH server currently advertises a number of key exchange, MAC, and host key algorithms that are considered weak or broken. The defaults should be tightened so a fresh installation passes a baseline SSH security audit out of the box.\n\n## Details\n\nRunning `ssh-audit` against a default deployment flags the following as `fail`:\n\n- **Key exchange**\n  - `ecdh-sha2-nistp256`\n  - `ecdh-sha2-nistp384`\n  - `ecdh-sha2-nistp521`\n- **MAC**\n  - `hmac-sha1`\n- **Host key**\n  - `ssh-rsa`\n\n## Reproduction\n\n```sh\ndocker run -it --rm positronsecurity/ssh-audit -p 2222 gitea.local\n```\n\n## Impact\n\nDefault deployments expose algorithms that are known-weak or deprecated upstream. The current workaround requires manually setting several `GITEA__server__SSH_SERVER_*` variables, which most users will never do.\n\n### Workaround\n\n```ini\n[server]\nSSH_SERVER_KEY_EXCHANGES = curve25519-sha256, diffie-hellman-group14-sha256\nSSH_SERVER_CIPHERS       = chacha20-poly1305@openssh.com, aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, aes256-gcm@openssh.com\nSSH_SERVER_MACS          = hmac-sha2-256-etm@openssh.com, hmac-sha2-256\n```\n\nThere is no exposed option to restrict host key algorithms, so `ssh-rsa` remains advertised.\n\n## Acceptance criteria\n\n- [ ] Default `SSH_SERVER_KEY_EXCHANGES`, `SSH_SERVER_CIPHERS`, and `SSH_SERVER_MACS` updated to the secure list above.\n- [ ] New `SSH_SERVER_HOST_KEY_ALGORITHMS` option added, with a default that excludes `ssh-rsa`.\n- [ ] Documentation updated to reflect the new defaults.\n- [ ] `ssh-audit` against a fresh install reports no `[fail]` entries.",
  "id": "GHSA-3m6q-h5gj-7mrw",
  "modified": "2026-04-22T20:37:21Z",
  "published": "2026-04-22T20:37:21Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/go-gitea/gitea/security/advisories/GHSA-3m6q-h5gj-7mrw"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/go-gitea/gitea"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Gitea has insecure default SSH settings"
}



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