CVE-2026-103059 in Gitea
Summary
by MITRE • 10/06/2026
When Gitea's built-in SSH server is enabled (`START_SSH_SERVER = true`), the presented public key was looked up with an SQL `LIKE` comparison of its encoded content, which is case-insensitive on some databases, including the default SQLite. An attacker who can construct a case variant of another user's registered RSA public key for which they can derive the private key could have that key matched to the victim's account and authenticate over SSH as that user. Keys are now looked up by fingerprint.
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Analysis
by VulDB Data Team • 10/07/2026
The vulnerability in Gitea stems from an implementation flaw within its built-in SSH server authentication mechanism, specifically when the service is enabled via the START_SSH_SERVER configuration flag. The core technical issue lies in how public keys are matched against registered user accounts during the authentication process. Instead of using a deterministic and unique identifier for key lookup, the system historically performed an SQL LIKE comparison on the encoded content of the presented public key. This approach introduced a critical security weakness because certain database engines, most notably SQLite which is often used as the default backend in Gitea deployments, perform case-insensitive string comparisons by default or under specific collation settings.
This case-insensitivity creates a scenario where an attacker can manipulate the byte representation of their own SSH public key to match the stored record of another user's key without possessing that user's private key initially. By constructing a valid RSA public key that is a case variant of a victim's registered key, and for which the attacker knows or can derive the corresponding private key material through mathematical properties related to the encoding format, the database query will return a false positive match. Consequently, the authentication system incorrectly associates the presented key with the victim's account ID rather than rejecting it as an unknown or unauthorized key.
The operational impact of this vulnerability is severe, allowing for complete remote code execution and identity impersonation via SSH access. An attacker who successfully exploits this flaw can authenticate to the Gitea instance as any user whose public key was stored in a database with case-insensitive matching capabilities. This bypasses all intended access controls, granting the attacker full administrative privileges if they target an administrator account or standard repository write access for regular users. The compromise undermines the integrity of version control operations, source code confidentiality, and potentially allows further lateral movement within connected infrastructure depending on how Gitea is integrated into broader CI/CD pipelines or server environments.
This flaw aligns with CWE-20 Improper Input Validation, as the system failed to properly validate that the input key uniquely identified a single authorized principal before granting access. It also relates to CWE-345 Insufficient Verification of Data Authenticity because the authentication mechanism relied on a non-deterministic string match rather than verifying cryptographic uniqueness. In terms of MITRE ATT&CK, this vulnerability facilitates Initial Access through Valid Accounts (T1078) and potentially Privilege Escalation if an attacker targets high-privilege accounts to gain broader system control.
The mitigation for this issue involves upgrading Gitea to a version where the SSH key lookup mechanism has been corrected to use cryptographic fingerprints instead of raw encoded string comparisons. Fingerprinting provides a fixed-length, case-sensitive hash that is unique to each specific public key material, eliminating ambiguity caused by encoding variations or database collation settings. Administrators should ensure their instances are updated immediately and verify that no unauthorized SSH sessions exist in the audit logs following any period where the vulnerable version was active with an enabled SSH server.