CVE-2026-4926
DoS in Pillarjs Path-To-Regexp 8.0.0 – 8.4.0
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HSummary
CVE-2026-4926 is a high-severity Uncontrolled Resource Consumption (CWE-400) vulnerability in Pillarjs Path-To-Regexp. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Endpoint Denial of Service (T1499); ranked in the top 47% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SC-5 (Denial-of-service Protection) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-4926 is a denial-of-service vulnerability in a routing component that generates regular expressions from route patterns. The issue arises when multiple sequential optional groups using curly brace syntax are present, such as `{a}{b}{c}:z`. This causes the generated regex to grow exponentially with the number of groups, leading to excessive resource consumption. The vulnerability is associated with CWE-400 (Uncontrolled Resource Consumption) and CWE-1333 (Inefficient Regular Expression Complexity) and has a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
A remote, unauthenticated attacker can exploit this vulnerability with low complexity and no user interaction by supplying a malicious route pattern containing many sequential optional groups. Successful exploitation results in denial of service through resource exhaustion, impacting availability but not confidentiality or integrity.
The vulnerability is fixed in version 8.4.0. Advisories recommend workarounds such as limiting the number of sequential optional groups in route patterns and avoiding the use of user-controlled input as route patterns. Additional details are available at https://cna.openjsf.org/security-advisories.html.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-16324
Vulnerability Data
Impact: A bad regular expression is generated any time you have multiple sequential optional groups (curly brace syntax), such as `{a}{b}{c}:z`. The generated regex grows exponentially with the number of groups, causing denial of service. Patches: Fixed in version 8.4.0.…
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Workarounds: Limit the number of sequential optional groups in route patterns. Avoid passing user-controlled input as route patterns.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover inefficient regex patterns via performance or static analysis.
SC-5 directly limits the effects of resource-exhaustion events that constitute uncontrolled consumption.
SC-6 enforces explicit allocation limits on resources, structurally preventing the weakness from occurring.
Development standards and tools can require safe regex construction and forbid known exponential patterns.
Process isolation confines resource consumption to separate domains, reducing blast radius without stopping the root flaw.
Input validation can constrain data that would otherwise trigger worst-case regex complexity.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Explicitly requires monitoring and maintaining resource capacity, directly addressing uncontrolled consumption to preserve availability.
Secure SDLC practices directly prevent inefficient regex via reviews, static analysis, and safe libraries.
Continuous monitoring of computing resources can detect resource exhaustion but does not itself enforce allocation limits.
Vulnerability identification processes can discover ReDoS issues in existing code but do not stop their introduction.
Resilience mechanisms such as avoiding single points of failure indirectly reduce impact of resource exhaustion.
Hardened configuration baselines can include resource quotas and limits that constrain consumption.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Resource-utilization monitoring and alerting on bottlenecks or overloads limits the impact of denial-of-service or resource-exhaustion attacks.
Security testing can detect and reject regex patterns with exponential worst-case complexity.
By continuously monitoring utilization, stress-testing peak loads, and maintaining documented plans to scale or throttle resources, the control directly limits an attacker’s ability to drive a system into uncontrolled resource exhaustion.
Pre-agreed severity-based prioritization and resource allocation during incident triage reduce the likelihood that an attacker-induced resource exhaustion will overwhelm the organization before corrective action is taken.
Business-continuity plans that include resource-management controls reduce the likelihood that an attacker can trigger uncontrolled resource consumption by forcing the system into a degraded or fallback state.
Defining RTOs and capacity requirements for ICT services during business-impact analysis forces organizations to provision sufficient resources and throttling mechanisms, reducing the likelihood that an attacker can induce denial-of-service through uncontrolled resource consumption.