CVE-2026-4923Network attack vector

Service interruption via repeated wildcard regex backtracking

Published Mar 26, 2026 · Updated Mar 26, 2026

Regular expression denial of service in PillarJS path-to-regexp 8.0.0 through 8.3.0 allows remote attackers to hang services via crafted paths. The toRegExpSource routine emits overlapping wildcard capture paths without preventing later wildcards from reconsidering text already consumed, causing catastrophic backtracking on crafted input. Reachability requires an application route with multiple wildcards and at least one parameter, with a nonterminal second wildcard; a long matching request can monopolize the JavaScript event loop and hang the service.

CVSS severity5.9
Medium
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in PillarJS path-to-regexp 8.0.0 through 8.3.0 allows remote attackers to hang services via crafted paths. The toRegExpSource routine emits overlapping wildcard capture paths without preventing later wildcards from reconsidering text already consumed, causing catastrophic backtracking on crafted input. Reachability requires an application route with multiple wildcards and at least one parameter, with a nonterminal second wildcard; a long matching request can monopolize the JavaScript event loop and hang the service.

The record

CVE
CVE-2026-4923
Published
Mar 26, 2026
Updated
Mar 26, 2026
Vendor
PillarJS
Product
path-to-regexp
Classifications
CWE-1333, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=8.0.0 <8.4.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

PillarJS · path-to-regexpversion=8.0.0 <8.4.0

Published CVSS scores

5.9GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1333Inefficient Regular Expression Complexity
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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