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High, CVSS 7.5amended

RE2JS: Quadratic-time denial of service in re2js lookbehind matching

CVE-2026-116795GHSA-gg6h-894w-4m9c

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (re2js 2.8.7), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm re2js

    Affected
    >= 2.2.0, < 2.8.7
    Fixed in
    2.8.7

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-116795: 0.46% estimated exploitation activity in the next 30 days; percentile 40.29 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Using the opt-in `LOOKBEHINDS` flag together with any repeated-matching API (`matcher().find()` in a loop, `matchAll()`, `split()`, `matcher().replaceAll()`) causes quadratic-time (Θ(n²)) matching, contradicting the library's own "linear time matching" guarantee. A single call with a 16,000-character input takes 36.7–38.7 seconds of CPU.

Description

Root cause In `build/index.cjs`, `Machine.match`: ```js let currentPos = this.prog.numLb > 0 ? 0 : pos; // ~line 1907 ... if (this.ncap === 0 && this.matched) break; // ~line 1953 ``` Any pattern containing a lookbehind sets `prog.numLb > 0`, which forces the scan to always restart at offset 0, regardless of the requested start position — the lookbehind automaton is re-seeded and the whole input is re-walked on every single `find()` call. The early-exit optimization that would otherwise stop at the first match only fires when `ncap === 0`, but every `Matcher`-based API (`find`/`matchAll`/`split`/`replaceAll`)…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from osv record GHSA-gg6h-894w-4m9c

  2. Revision 1 · created ·

    Published from ghsa record GHSA-gg6h-894w-4m9c

Agent brief

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# Patch Next advisory brief: CVE-2026-116795

Advisory: RE2JS: Quadratic-time denial of service in re2js lookbehind matching
IDs: CVE-2026-116795, GHSA-gg6h-894w-4m9c
Record: https://patchnext.com/advisories/cve-2026-116795 (revision 2, source checked 29 Oct 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: re2js 2.8.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm re2js: affected >= 2.2.0, < 2.8.7; fixed in 2.8.7

## Suggested inspection (read-only)
- `npm ls re2js --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on re2js.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-gg6h-894w-4m9c (OSV record GHSA-gg6h-894w-4m9c lists affected ranges: npm re2js >=2.2.0 <2.8.7 (fixed))
- Verified: https://github.com/advisories/GHSA-gg6h-894w-4m9c (GitHub-reviewed advisory GHSA-gg6h-894w-4m9c lists affected ranges: npm re2js >=2.2.0 <2.8.7)

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