CVE-2026-4926: Impact: A bad regular expression is generated any time you have multiple sequential optional groups (curly br

Q: How do I fix CVE-2026-4926?

path-to-regexp: upgrade to 8.4.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-4926 being exploited?

CVE-2026-4926 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-4926 affect?

CVE-2026-4926 affects path-to-regexp. Severity is high (CVSS 7.5). 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.

Q: How urgent is CVE-2026-4926?

Priority 45/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-4926 is a high-severity flaw (CVSS 7.5) affecting path-to-regexp. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.8% (top 43%)
CISA exploited list	No
Weakness	CWE-400, CWE-1333
Published	2026-03-26
Last modified	2026-09-09

Publisher (CNA): openjs · Vendor: pillarjs

Last updated 2026-09-09 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-26 19:17 UTCPublished CVE record published
2026-09-09 13:20 UTCUpdated Record last modified

pillarjs path-to-regexp UPGRADE

Affected: >= 8.0.0 and < 8.4.0

Fixed in: 8.4.0

Safe to downgrade to: a release before 8.0.0

1. Check installed version

npm ls path-to-regexp

2. UPGRADE to 8.4.0

npm install path-to-regexp@">=8.4.0"

3. If no update is available yet, DOWNGRADE to a release before 8.0.0

npm view path-to-regexp versions npm install path-to-regexp@"<8.0.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-4926?

path-to-regexp: upgrade to 8.4.0. Exact commands for each OS are on this page.

Is CVE-2026-4926 being exploited?

CVE-2026-4926 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-4926 affect?

CVE-2026-4926 affects path-to-regexp. Severity is high (CVSS 7.5). 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.

How urgent is CVE-2026-4926?

Priority 45/100. High severity; Remotely exploitable, no login, no user action

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CVE-2026-4867 HIGH 7.5 UPGRADE Impact: A bad regular expression is generated any time you have three or more parameters within a single segm

References

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