CVE-2011-1027 in cgit
Summary
by MITRE
Off-by-one error in the convert_query_hexchar function in html.c in cgit.cgi in cgit before 0.8.3.5 allows remote attackers to cause a denial of service (infinite loop) via a string composed of a % (percent) character followed by invalid hex characters, as demonstrated by a %gg sequence.
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Analysis
by VulDB Data Team • 10/20/2021
The vulnerability identified as CVE-2011-1027 represents a critical off-by-one error within the cgit web-based git repository viewer software. This flaw exists in the convert_query_hexchar function located in the html.c source file of cgit.cgi, specifically affecting versions prior to 0.8.3.5. The issue manifests when processing URL-encoded query parameters that contain percent-encoded sequences, creating a scenario where the software fails to properly validate input boundaries during hexadecimal character conversion operations.
The technical nature of this vulnerability stems from improper boundary checking within the hex character conversion routine. When cgit encounters a string beginning with a percent character followed by invalid hexadecimal characters such as the sequence %gg, the convert_query_hexchar function fails to correctly handle the edge case where the input does not conform to valid hexadecimal encoding. This off-by-one error causes the parsing logic to enter an infinite loop as it attempts to process the malformed input without proper termination conditions, effectively consuming system resources and rendering the service unavailable to legitimate users.
This vulnerability directly maps to CWE-129, which describes improper validation of array index values, and specifically relates to CWE-131, which covers incorrect calculation of buffer or array bounds. The operational impact of this denial of service condition is severe as it allows remote attackers to exploit the flaw without requiring authentication or special privileges. The infinite loop consumes CPU resources indefinitely, potentially leading to system instability, resource exhaustion, and complete service unavailability for legitimate users attempting to access git repositories through the affected cgit interface.
The attack vector is straightforward and accessible, requiring only a specially crafted URL containing the malformed percent-encoding sequence to trigger the vulnerable code path. This makes the vulnerability particularly dangerous in public-facing web applications where cgit is deployed. The flaw demonstrates poor input validation practices and highlights the importance of proper boundary checking in parsing functions that handle user-provided data. Organizations utilizing cgit for git repository browsing should immediately implement the available patch version 0.8.3.5 or later to address this vulnerability, as the fix involves correcting the boundary conditions in the hex character conversion logic to properly handle invalid input sequences and prevent the infinite loop condition.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion. The vulnerability also demonstrates characteristics of T1210, involving exploitation of software vulnerabilities for privilege escalation or service disruption. The remediation strategy focuses on input validation improvements and proper error handling mechanisms that prevent malformed data from causing indefinite processing loops in the application's parsing routines.