CVE-2026-4926 — path-to-regexp
HIGHCVE-2026-4926 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in path-to-regexp. A fix is available for path-to-regexp — see the affected versions and patch details below.
path-to-regexp vulnerable to Denial of Service via sequential optional groups
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-4926.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-4926 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,166 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
path-to-regexpnpmDescription
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.
Workarounds:
Limit the number of sequential optional groups in route patterns. Avoid passing user-controlled input as route patterns.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | path-to-regexp | ≥ 8.0.0&&< 8.4.0 | 8.4.0npm install path-to-regexp@8.4.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for path-to-regexp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update path-to-regexp to 8.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-4926 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-4926 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-4926. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This is an Important flaw in `path-to-regexp` that can lead to a Denial of Service. The vulnerability occurs when specially crafted input containing multiple sequential optional groups is used to generate regular expressions, causing exponential resource consumption. The Red Hat Advanced Cluster Security is not…
| Product | Fixed in | Advisory |
|---|---|---|
| Cryostat 4 on RHEL 9 | cryostat/cryostat-openshift-console-plugin-rhel9:4.2.0-9 | RHSA-2026:17789 |
| Red Hat Ansible Automation Platform 2.5 for RHEL 8 | automation-gateway-0:2.5.20260422-3.el8ap | RHSA-2026:24761 |
| Red Hat Ansible Automation Platform 2.6 for RHEL 9 | automation-platform-ui-0:2.6.9-1.el9ap | RHSA-2026:24762 |
| Migration Toolkit for Virtualization 2.1 | migration-toolkit-virtualization/mtv-console-plugin-rhel9:1779139872 | RHSA-2026:19409 |
| Migration Toolkit for Virtualization 2.9 | migration-toolkit-virtualization/mtv-console-plugin-rhel9:1778927462 | RHSA-2026:19410 |
| Red Hat Ansible Automation Platform 2.6 | ansible-automation-platform-tech-preview/mcp-server-rhel9:1777386606 | RHSA-2026:13545 |
| Red Hat Ansible Automation Platform 2.6 | ansible-automation-platform-26/gateway-rhel9:1779773804 | RHSA-2026:24866 |
| Red Hat Developer Hub 1.8 | rhdh/rhdh-hub-rhel9:1776784286 | RHSA-2026:9742 |
Frequently Asked Questions
Is CVE-2026-4926 in your dependencies?
O3 Security finds CVE-2026-4926 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.