CVE-2026-81159 Overview
CVE-2026-81159 is an observable timing discrepancy vulnerability in the Drupal Commerce CyberSource module. The flaw affects Commerce CyberSource versions 0.0.0 through 1.10.0. An attacker can measure response-time differences to infer sensitive values, enabling brute-force attacks against protected data. The weakness is categorized under CWE-208: Observable Timing Discrepancy and is exploitable over the network without authentication or user interaction.
Critical Impact
Attackers can leverage timing side channels in Commerce CyberSource up to 1.10.0 to brute-force sensitive comparison operations, potentially compromising integrity of validation checks tied to payment integration.
Affected Products
- Drupal Commerce CyberSource module versions 0.0.0 through 1.10.0
- Drupal sites using the CyberSource payment integration module
- Any Commerce deployment with Commerce CyberSource <= 1.10.0 installed
Discovery Timeline
- 2026-09-02 - CVE-2026-81159 published to NVD
- 2026-09-02 - Last updated in NVD database
Technical Details for CVE-2026-81159
Vulnerability Analysis
The Commerce CyberSource module performs comparisons on sensitive values using operations whose execution time varies with input. This behavior enables an attacker to measure response latency across many requests and infer bytes of a secret one position at a time. The vulnerability applies to network-facing endpoints exposed by the module, meaning remote exploitation is possible without prior authentication. Successful exploitation compromises integrity, though confidentiality and availability are not directly affected according to the published scoring.
Root Cause
The underlying weakness [CWE-208] arises when code compares secrets using non-constant-time routines such as standard string equality. Each mismatched byte short-circuits the comparison faster than a correct byte, producing a measurable timing signal. Commerce CyberSource up to 1.10.0 contains such a comparison in a security-sensitive code path connected to payment processing validation.
Attack Vector
An unauthenticated remote attacker sends repeated crafted requests to the affected Drupal endpoint. The attacker records precise response times and applies statistical analysis to distinguish correct from incorrect guesses. High attack complexity reflects the need for stable network measurements and significant request volume. Refer to the Drupal Security Advisory 2026-106 for vendor-supplied technical detail.
No public exploit code or proof-of-concept has been published for this issue at the time of writing.
Detection Methods for CVE-2026-81159
Indicators of Compromise
- High-volume repeated requests to Commerce CyberSource endpoints from a single source or small set of IPs
- Sequential requests differing only in a single field value, consistent with byte-by-byte guessing
- Elevated request rates targeting payment-related paths without corresponding legitimate checkout flows
Detection Strategies
- Baseline normal request rates against Commerce CyberSource endpoints and alert on statistical deviations
- Inspect web server and Drupal watchdog logs for repeated failed validations from the same origin
- Correlate response-time patterns with client IP to identify timing-oracle probing behavior
Monitoring Recommendations
- Enable verbose logging on Drupal payment routes and forward logs to a centralized analytics platform
- Monitor for anomalous outbound traffic from Drupal hosts following suspicious probing sequences
- Track module version inventory to confirm all Commerce CyberSource installs are above 1.10.0
How to Mitigate CVE-2026-81159
Immediate Actions Required
- Identify all Drupal sites running the Commerce CyberSource module and record installed versions
- Upgrade Commerce CyberSource to a version above 1.10.0 as directed by the vendor advisory
- Restrict network access to payment endpoints where feasible, limiting exposure during patch rollout
- Review recent web logs for signs of high-volume automated probing of CyberSource routes
Patch Information
Drupal has published remediation guidance in Drupal Security Advisory 2026-106. Administrators should apply the fixed release identified in that advisory and clear caches after upgrade. Verify module version through drush pm:list or the Drupal admin modules page after patching.
Workarounds
- Deploy a web application firewall rule to rate-limit requests to Commerce CyberSource endpoints
- Enforce IP-based throttling and CAPTCHA challenges on payment submission routes
- Temporarily disable the Commerce CyberSource module if a compatible fixed release cannot be deployed immediately
# Configuration example: verify installed module version and update
drush pm:list --type=module --status=enabled | grep commerce_cybersource
composer update drupal/commerce_cybersource
drush updatedb -y
drush cache:rebuild
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
