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No exploitation reportedFix available

CVE-2026-4867

No exploitation reported by the sources we read.

  • Published2026-03-26
  • Fixed in8.0.0 · 6.3.0 · 3.3.0 · 1.9.0 · 0.1.13 · 0.1.10
  • WeaknessCWE-1333

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Impact: A bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not a period (.). For example, /:a-:b-:c or /:a-:b-:c-:d. The backtrack protection added in path-to-regexp@0.1.12 only prevents ambiguity for two parameters. With three or more, the generated lookahead does not block single separator characters, so capture groups overlap and cause catastrophic backtracking. Patches: Upgrade to path-to-regexp@0.1.13 Custom regex patterns in route definitions (e.g., /:a-:b([^-/]+)-:c([^-/]+)) are not affected because they override the default capture group. Workarounds: All versions can be patched by providing a custom regular expression for parameters after the first in a single segment. As long as the custom regular expression does not match the text before the parameter, you will be safe. For example, change /:a-:b-:c to /:a-:b([^-/]+)-:c([^-/]+). If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length.

Timeline

dates in UTC
  1. 2026-03-2617:16CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-4867?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-4867?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

OSV · NVD
Pillarjs path-to-regexp
BranchAffectedFixed in
8.0≥ 7.0.0, < 8.0.08.0.0
6.3≥ 4.0.0, < 6.3.06.3.0
3.3≥ 2.0.0, < 3.3.03.3.0
1.9≥ 0.2.0, < 1.9.01.9.0
0.1< 0.1.130.1.13
0.1< 0.1.100.1.10

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • RHSA-2026:34342 Red Hat Product Security12 products fixed

    Red Hat Security Advisory: Cluster Observability Operator 1.5.0

Full record on NVD

Fix

  1. Update Pillarjs path-to-regexp to 8.0.0 · 6.3.0 · 3.3.0 · 1.9.0 · 0.1.13 · 0.1.10
  2. Vendor fix Red Hat Product Security RHSA-2026:34342 · 12 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. For details on how to apply this update, refer to: https://access.redhat.com/articles/11258
  3. Workaround from the vendor Red Hat Product Security RHSA-2026:34342 · 97 productsTo mitigate this issue, applications using `path-to-regexp` can implement custom regular expressions for parameters beyond the first in a single URL segment. For example, a route like `/:a-:b-:c` can be rewritten as `/:a-:b([^-/]+)-:c([^-/]+)`. Alternatively, limiting the maximum length of incoming…

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionnone2026-03-26
  • OpenCVESSVC decisionnone—
  • CNACVSS 3.17.5read 2026-10-23
  • CNAweakness (CWE)CWE-1333read 2026-10-23
  • FIRST EPSSEPSS score0.6 %2026-10-22
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published
2026-03-26
Last Modified
2026-06-17
NVD status
Analyzed

Frequently asked questions

What is CVE-2026-4867?

Impact: A bad regular expression is generated any time you have three or more parameters within a single segment, separated by something that is not a period (.). For example, /:a-:b-:c or /:a-:b-:c-:d. The backtrack protection added in path-to-regexp@0.1.12 only prevents ambiguity for two parameters. With three or more, the generated lookahead does not block single separator characters, so capture groups overlap and cause catastrophic backtracking. Patches: Upgrade to path-to-regexp@0.1.13 Custom regex patterns in route definitions (e.g., /:a-:b([^-/]+)-:c([^-/]+)) are not affected because they override the default capture group. Workarounds: All versions can be patched by providing a custom regular expression for parameters after the first in a single segment. As long as the custom regular expression does not match the text before the parameter, you will be safe. For example, change /:a-:b-:c to /:a-:b([^-/]+)-:c([^-/]+). If paths cannot be rewritten and versions cannot be upgraded, another alternative is to limit the URL length.

Is CVE-2026-4867 actively exploited?

Active exploitation of CVE-2026-4867 has not been confirmed. Its EPSS score was 0.6% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-4867?

CVE-2026-4867 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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