CVE-2026-16270 Overview
CVE-2026-16270 affects Open Mercato, an open-source commerce platform. The application fails to validate regular expression patterns supplied when creating regex-based field rules. An authenticated user with privileges to create regex rules can insert a pattern vulnerable to catastrophic backtracking. When matched against a crafted input string, the regex engine consumes excessive CPU time. This condition results in Regular Expression Denial of Service (ReDoS), tracked under [CWE-1333]. The issue was resolved in Open Mercato version 0.6.4.
Critical Impact
An authenticated attacker with rule-creation privileges can plant an unsafe regex that triggers denial of service through CPU exhaustion when specific strings are evaluated against the rule.
Affected Products
- Open Mercato versions prior to 0.6.4
- Deployments exposing regex rule configuration to authenticated users
- Commerce environments processing user-supplied strings through configured regex rules
Discovery Timeline
- 2026-07-22 - CVE-2026-16270 published to NVD
- 2026-07-22 - Last updated in NVD database
Technical Details for CVE-2026-16270
Vulnerability Analysis
Open Mercato allows privileged users to define regex-based validation or matching rules on fields. The application accepts these regex patterns without checking their computational safety. Regex engines using backtracking algorithms can enter pathological states when evaluating specific patterns against crafted inputs. Patterns containing nested quantifiers or overlapping alternations, such as (a+)+$, exhibit exponential time complexity in the worst case. When a string matching this pathological structure is supplied, the matching operation blocks the worker thread. Sustained submission of such strings exhausts CPU resources and denies service to legitimate users.
Root Cause
The root cause is missing validation of user-supplied regular expressions before storing them as active rules. Open Mercato trusts the pattern author to provide safe expressions, but the platform does not enforce complexity limits, timeouts, or safe-regex analysis. The weakness is classified as [CWE-1333], Inefficient Regular Expression Complexity.
Attack Vector
Exploitation requires network access and high privileges, since only users authorized to create regex rules can plant a malicious pattern. Once the rule is stored, any request path that evaluates the rule against attacker-controlled input triggers the denial of service. No user interaction is needed on the victim side. The confidentiality and integrity of data are not affected, but availability of the affected service can be degraded significantly.
No verified proof-of-concept code has been published. Technical details are available in the CERT Security Advisory CVE-2026-16270 and GitHub Pull Request #1996.
Detection Methods for CVE-2026-16270
Indicators of Compromise
- Sustained high CPU usage on Open Mercato worker processes without a corresponding rise in request volume
- Request timeouts or thread pool exhaustion tied to endpoints that evaluate regex rules
- Recently created or modified regex rules containing nested quantifiers such as (a+)+, (.*)*, or (a|a)+
Detection Strategies
- Audit stored regex rules for patterns known to cause catastrophic backtracking using static analyzers such as safe-regex or redos-detector
- Correlate slow request traces with the specific rule identifiers evaluated during those requests
- Track administrative actions that create or update regex rules and flag anomalous changes by user
Monitoring Recommendations
- Alert on request processing times exceeding a defined threshold on endpoints that invoke regex evaluation
- Monitor per-user rule-creation events and require review for privileged rule changes
- Log the full regex pattern on rule creation to support forensic review after suspected abuse
How to Mitigate CVE-2026-16270
Immediate Actions Required
- Upgrade Open Mercato to version 0.6.4 or later, which introduces regex validation
- Review all existing regex rules and remove or replace patterns containing nested quantifiers
- Restrict rule-creation privileges to a minimal set of trusted administrators
Patch Information
The fix is delivered in Open Mercato 0.6.4. The relevant code changes are tracked in GitHub Pull Request #1996. Refer to the CERT Security Advisory CVE-2026-16270 for the official disclosure and remediation guidance.
Workarounds
- Temporarily revoke the privilege that permits creating or editing regex rules until the upgrade is applied
- Apply an application-level timeout on regex evaluation to bound worst-case execution time
- Pre-screen submitted patterns with a safe-regex library before persisting them as rules
# Example: pre-screen a regex with safe-regex before saving
npx safe-regex "$USER_SUPPLIED_PATTERN" && echo "safe" || echo "reject"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
