CVE-2020-13333 in GitLab
Summary
by MITRE • 10/06/2020
A potential DOS vulnerability was discovered in GitLab versions 13.1, 13.2 and 13.3. The api to update an asset as a link from a release had a regex check which caused exponential number of backtracks for certain user supplied values resulting in high CPU usage.
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Analysis
by VulDB Data Team • 11/16/2020
The vulnerability CVE-2020-13333 represents a denial of service weakness in GitLab versions 13.1 through 13.3 that stems from an inadequate regular expression implementation within the release asset update functionality. This issue manifests when users attempt to modify a release asset that is configured as a link, triggering a regex validation process that exhibits pathological behavior under specific input conditions. The flaw resides in the regular expression engine's handling of certain maliciously crafted input patterns that cause exponential backtracking during pattern matching operations.
The technical mechanism behind this vulnerability involves the use of regular expressions with inefficient backtracking algorithms that can spiral into exponential time complexity when processing particular input strings. When a user supplies asset link data that triggers the vulnerable regex pattern, the system's CPU utilization spikes dramatically as the regex engine attempts to match the input against the pattern through an exponential number of potential backtracking paths. This behavior aligns with CWE-1321, which specifically addresses regular expression denial of service vulnerabilities arising from catastrophic backtracking scenarios. The vulnerability affects the GitLab release management API endpoint responsible for updating asset links, making it susceptible to exploitation through crafted input values that cause the system to consume excessive computational resources.
The operational impact of this vulnerability extends beyond simple resource exhaustion, as it can effectively render GitLab instances unavailable to legitimate users during attack execution. Attackers can leverage this weakness to consume excessive CPU cycles, potentially leading to system instability, performance degradation, or complete service unavailability. The vulnerability particularly affects organizations relying on GitLab for release management workflows where asset links are frequently updated, as even a single malicious request can trigger sustained high CPU usage. This represents a significant concern for continuous integration and deployment environments where GitLab serves as a critical infrastructure component, as the denial of service can disrupt automated build processes and release cycles.
Mitigation strategies for CVE-2020-13333 primarily involve upgrading to GitLab versions 13.4 or later where the vulnerable regex implementation has been corrected. Organizations should also implement input validation measures at the network level, including rate limiting and request filtering to prevent exploitation attempts. The fix typically involves rewriting the vulnerable regular expression to eliminate exponential backtracking possibilities, often by using more efficient regex patterns or switching to alternative validation approaches. Security teams should monitor for exploitation attempts through log analysis and implement intrusion detection systems that can identify anomalous API usage patterns. This vulnerability demonstrates the importance of regular security updates and proper input validation practices, aligning with ATT&CK technique T1499.004 for network denial of service and emphasizing the need for robust regex implementation practices to prevent similar vulnerabilities in software systems.