GHSA-j3q9-mxjg-w52f CVE-2026-4926

path-to-regexp vulnerable to Denial of Service via sequential optional groups

High npm

Severity: 7.5 / 10; High · CVSS 3.1
Exploit chance (EPSS): 0.80%; Chance of exploitation in the next 30 days. Higher than 56.78% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-400 Uncontrolled Resource Consumption; CWE-1333 Inefficient Regular Expression Complexity
Fix: 8.4.0; Upgrade path-to-regexp to this version or later

Description

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 versions

npm

Package	Vulnerable	Fixed in
path-to-regexp	`>= 8.0.0, < 8.4.0`	`8.4.0`
path-to-regexp	`>= 8.0.0, < 8.4.0`	`8.4.0`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

path-to-regexp npm → `8.4.0`

npm

npm install path-to-regexp@8.4.0

yarn

yarn add path-to-regexp@8.4.0

pnpm

pnpm add path-to-regexp@8.4.0

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-400: Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource.

How to prevent it

Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Implementation: Ensure that all failures in resource allocation place the system into a safe posture.

CWE-1333: Inefficient Regular Expression Complexity

The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

How to prevent it

Architecture and Design: Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
System Configuration: Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
Implementation: Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
Implementation: Limit the length of the input that the regular expression will process.

References

Advisories

Packages

github.com/pillarjs/path-to-regexp

Timeline

Mar 26, 2026 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-27v5-c462-wpq7 path-to-regexp vulnerable to Regular Expression Denial of Service via multiple wildcards	Medium	Also affects path-to-regexp
GHSA-rhx6-c78j-4q9w path-to-regexp contains a ReDoS	High	Also affects path-to-regexp
GHSA-37ch-88jc-xwx2 path-to-regexp vulnerable to Regular Expression Denial of Service via multiple route parameters	High	Also affects path-to-regexp
GHSA-cggf-277g-3q54 pypdf has possible large memory usage when parsing page tree	High	Same weakness, CWE-400
GHSA-3g3m-2fjr-6pw4 Glob: AbortSignal cancellation bypass allows post-timeout filesystem traversal	Medium	Same weakness, CWE-400
GHSA-42gh-23hr-vphw pypdf has possible long runtimes when retrieving page labels	High	Same weakness, CWE-400
GHSA-4vqv-7265-gm2w pypdf has possible large memory usage for exceptions in strict mode	High	Same weakness, CWE-400
GHSA-62m5-6wh8-28x7 pypdf has possible long runtimes/large memory usage for encrypted PDF files	High	Same weakness, CWE-400

Credits: UlisesGascon, blakeembrey, uug4na

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