ts-deepmerge: Prototype Method Override leads to DoS

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-12644: 0.51% estimated exploitation activity in the next 30 days; percentile 43.30 (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.

Versions of the package ts-deepmerge before 8.0.0 are vulnerable to Uncaught Exception due to the improper handling of built-in Object.prototype methods (such as toString, valueOf). When user-controlled input contains these keys with non-function values, the resulting merged object becomes broken — any string context operation throws a TypeError, crashing the application.

Published by the source

19 Jun 2026, 06:31 UTC

Last modified by the source

19 Jun 2026, 21:56 UTC

Source last checked

26 Oct 2026, 12:56 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-87mf-gv2c-c62c

2. Revision 2 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-87mf-gv2c-c62c

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# Patch Next advisory brief: CVE-2026-12644

Advisory: ts-deepmerge: Prototype Method Override leads to DoS
IDs: CVE-2026-12644, GHSA-87mf-gv2c-c62c
Record: https://patchnext.com/advisories/cve-2026-12644 (revision 3, source checked 26 Oct 2026, 12:56 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ts-deepmerge 8.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm ts-deepmerge: affected < 8.0.0; fixed in 8.0.0

## Suggested inspection (read-only)
- `npm ls ts-deepmerge --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 ts-deepmerge.
- 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-87mf-gv2c-c62c (OSV record GHSA-87mf-gv2c-c62c lists affected ranges: npm ts-deepmerge >=0 <8.0.0 (fixed))
- Verified: https://github.com/advisories/GHSA-87mf-gv2c-c62c (GitHub-reviewed advisory GHSA-87mf-gv2c-c62c lists affected ranges: npm ts-deepmerge >=0 <8.0.0)

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