{"id":"GHSA-3m6q-h5gj-7mrw","aliases":["GO-2026-5091"],"url":"https://o3.security/vulnerability/GHSA-3m6q-h5gj-7mrw","summary":"Gitea has insecure default SSH settings","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.","published":"2026-04-22T20:37:21Z","modified":"2026-06-25T18:56:39.025404508Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"code.gitea.io/gitea","fixedVersion":"1.25.0"}],"fix":null,"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-06-25T18:56:39.025404508Z"}}