CVE-2026-1403 in GitLab
Summary
by MITRE • 10/08/2026
GitLab has remediated an issue in GitLab CE/EE affecting all versions from 11.7 before 18.8.9, 18.9 before 18.9.5, and 18.10 before 18.10.3 that when importing CSV files could have allowed an authenticated user to cause denial of service to Sidekiq workers due to improper validation of CSV file structure.
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Analysis
by VulDB Data Team • 10/08/2026
GitLab has addressed a critical security vulnerability impacting both Community Edition and Enterprise Edition across multiple version ranges, specifically versions prior to 18.8.9 for the 18.7 series, before 18.9.5 for the 18.9 series, and before 18.10.3 for the 18.10 series. This flaw resides within the CSV import functionality, a feature commonly used by administrators and developers to bulk-upload data into issues, merge requests, or other project entities. The core technical deficiency involves improper validation of the structural integrity of uploaded CSV files before they are processed by the backend worker infrastructure. When an authenticated user submits a malformed or excessively large CSV file with irregularities in column counts or row structures, the system fails to reject it early enough in the ingestion pipeline. Instead, the flawed logic attempts to parse and process these invalid records through Sidekiq workers, which are responsible for handling background jobs such as data processing and notifications.
The operational impact of this vulnerability is primarily a denial of service condition targeting the GitLab application's performance stability rather than confidentiality or integrity in the traditional sense. Because the validation occurs after the file has been accepted into the queueing system, Sidekiq workers consume significant CPU and memory resources attempting to parse rows that do not conform to expected schemas. This can lead to worker exhaustion, where available threads are tied up processing invalid data, thereby preventing legitimate background jobs from executing. In severe cases, this resource contention can cause the entire GitLab instance to become unresponsive or slow down significantly for all users, effectively disrupting development workflows and CI/CD pipelines that rely on timely execution of queued tasks. The vulnerability is classified under CWE-20 as Improper Input Validation because the application does not adequately sanitize or verify input data before processing it.
From a threat modeling perspective aligned with MITRE ATT&CK frameworks, this issue maps to T1496 Resource Hijacking, where an attacker consumes system resources to degrade service availability for other users. It also relates to T1053 Scheduled Task/Job as the exploitation leverages the background job processing mechanism of Sidekiq. While the attack requires authentication, which limits its scope compared to remote unauthenticated exploits, it poses a significant risk in environments where user accounts may be compromised or shared among many individuals with varying levels of technical awareness. An attacker could intentionally craft CSV files designed to trigger maximum parsing overhead, leading to sustained degradation of service quality and potential data loss if workers crash during critical operations like database transactions associated with the import process.
Mitigation strategies for this vulnerability are straightforward but require immediate action due to its impact on system stability. Administrators must upgrade their GitLab instances to version 18.8.9 or later, 18.9.5 or later, or 18.10.3 or later, depending on the current release track in use. These patched versions include enhanced validation logic that checks CSV structure and size constraints before enqueuing jobs for Sidekiq processing. In addition to upgrading, organizations should implement strict file upload policies at the network perimeter using web application firewalls to limit the maximum allowed size of uploaded files and restrict content types where possible. Monitoring sidekiq worker logs for high CPU usage or repeated parsing errors can help detect attempted exploitation in real-time while patching efforts are underway. Regular audits of user permissions ensure that only trusted individuals have access to bulk import features, reducing the attack surface available to potential insiders or compromised accounts.