CVE-2026-56657 in Gitea
Summary
by MITRE • 08/13/2026
Gitea SSH Key Parser Denial of Service
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Analysis
by VulDB Data Team • 08/13/2026
The Gitea SSH key parser denial of service vulnerability represents a critical security flaw in the open source Git service platform that can be exploited to disrupt system availability. This vulnerability specifically affects the SSH key parsing functionality within Gitea's authentication and authorization mechanisms, where malformed or specially crafted SSH public keys can trigger infinite loops or resource exhaustion conditions during processing. The issue stems from insufficient input validation and sanitization within the SSH key parser component that handles public key operations for user authentication and repository access control.
The technical implementation of this vulnerability resides in the parsing logic that processes SSH public keys submitted by users during authentication attempts or repository operations. When an attacker submits a malformed SSH key structure that contains recursive references, malformed data sequences, or specially crafted patterns designed to exploit parsing loops, the parser enters into resource-intensive processing states that can consume excessive CPU cycles and memory resources. This behavior aligns with CWE-400 vulnerability classification related to unchecked resource consumption and represents a classic denial of service vector through resource exhaustion.
From an operational perspective this vulnerability presents significant risk to Gitea deployments as it allows attackers to cause system instability and service disruption without requiring authentication or privileged access. The impact extends beyond simple service interruption to potentially affecting repository operations, user authentication flows, and overall platform availability for legitimate users. Attackers can leverage this weakness by submitting malicious SSH keys that trigger the vulnerable parsing routines repeatedly, leading to sustained denial of service conditions that can affect multiple users simultaneously.
The attack surface encompasses all Gitea installations that accept SSH key submissions, including those used for repository cloning, pushing operations, and user authentication scenarios. This vulnerability affects various deployment configurations including self-hosted instances, cloud deployments, and enterprise installations where SSH key management is integral to the platform's security model. The exploitation requires minimal technical expertise and can be automated through simple scripts that generate malformed key structures designed to trigger the parsing loops.
Security mitigations for this vulnerability involve implementing robust input validation mechanisms within the SSH key parsing component to detect and reject malformed or suspicious key structures before processing begins. Organizations should apply the latest security patches provided by Gitea maintainers, which typically include enhanced validation routines and improved error handling for SSH key parsing operations. Additionally, deploying rate limiting controls and monitoring systems that can detect unusual parsing patterns will help identify potential exploitation attempts. The remediation process should also include comprehensive testing of SSH key handling functionality to ensure that the patched implementation properly handles edge cases and malformed inputs without consuming excessive system resources.
This vulnerability demonstrates the importance of proper input validation in cryptographic and authentication components, aligning with ATT&CK technique T1499 related to network denial of service attacks. Organizations should also consider implementing principle of least privilege controls for SSH key management operations and regularly audit their authentication systems for similar parsing vulnerabilities that could lead to resource exhaustion conditions. The incident highlights the critical need for defensive programming practices in security-sensitive components and proper error handling mechanisms that prevent malformed input from causing system instability or resource consumption issues.