decode-uri-component vulnerable to denial of service via quadratic replacement of percent-encoded runs

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-118664: 0.32% estimated exploitation activity in the next 30 days; percentile 24.84 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary `decodeUriComponent()` takes quadratic time on malformed input that has many distinct percent-encoded runs. A single unauthenticated request of about 224 KB can block the Node.js event loop for about 20 seconds. Version 0.5.0, the release that fixed CVE-2026-45822, is affected.

Details When native decodeURIComponent throws, `decodeUriComponent()` falls back to `customDecodeURIComponent` (`index.js:122`). That function: 1. Scans the input for every run of percent-encoded bytes (e.g. `%C3%A5`) and stores each distinct run, with its decoded value, in a lookup table (`index.js:130-144`). 2. Runs one full-string `input.replace(new RegExp(key, 'g'), …)` per table entry (`index.js:154`). With K distinct runs in an input of length L, that's K regex compilations and K full scans of the string, so O(K·L). An attacker controls both K and L, and K grows with L. One malformed sequence such as a trailing `%zz` is enough to force the fallback path. The 0.5.0 fix for CVE-2026-45822…

Published by the source

29 Oct 2026, 16:41 UTC

Last modified by the source

29 Oct 2026, 17:00 UTC

Source last checked

30 Oct 2026, 06:00 UTC

1. Revision 2 · amended · 30 Oct 2026

   Amended from osv record GHSA-qr28-fpjm-wq7f

2. Revision 1 · created · 29 Oct 2026

   Published from ghsa record GHSA-qr28-fpjm-wq7f

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# Patch Next advisory brief: CVE-2026-118664

Advisory: decode-uri-component vulnerable to denial of service via quadratic replacement of percent-encoded runs
IDs: CVE-2026-118664, GHSA-qr28-fpjm-wq7f
Record: https://patchnext.com/advisories/cve-2026-118664 (revision 2, source checked 30 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 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: decode-uri-component 0.5.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm decode-uri-component: affected < 0.5.1; fixed in 0.5.1

## Suggested inspection (read-only)
- `npm ls decode-uri-component --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 decode-uri-component.
- 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://github.com/advisories/GHSA-qr28-fpjm-wq7f (GitHub-reviewed advisory GHSA-qr28-fpjm-wq7f lists affected ranges: npm decode-uri-component >=0 <=0.5.0)
- Verified: https://osv.dev/vulnerability/GHSA-qr28-fpjm-wq7f (OSV record GHSA-qr28-fpjm-wq7f lists affected ranges: npm decode-uri-component >=0 <0.5.1 (fixed))

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