@stablelib/cbor: Prototype poisoning via __proto__ map keys in CBOR decoding

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-106448: 0.40% estimated exploitation activity in the next 30 days; percentile 34.39 (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 @stablelib/cbor decodes CBOR maps into ordinary JavaScript objects and assigns attacker-controlled keys directly onto those objects. A CBOR map key named proto therefore changes the prototype of the decoded object instead of becoming an ordinary data property. Details The decoder builds map results with a plain {} and then stores attacker-controlled keys using bracket assignment. That is unsafe for special property names. In JavaScript, assigning to obj["proto"] on a normal object does not create a plain own property. It invokes the built-in proto setter and replaces the object’s prototype if the supplied value is an object or null. As a result, a CBOR payload containing a map entry like: key: "proto" value: { isAdmin: true } does not decode to an object with an own property called proto. It decodes to an object whose prototype is now attacker-controlled. Any code that later reads properties through normal lookup will see inherited attacker-supplied values. PoC Impact Any…

Published by the source

4 Apr 2026, 04:24 UTC

Last modified by the source

7 Oct 2026, 10:56 UTC

Source last checked

26 Oct 2026, 12:47 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-w48f-fwg7-ww6p

2. Revision 2 · amended · 25 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-w48f-fwg7-ww6p

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# Patch Next advisory brief: CVE-2026-106448

Advisory: @stablelib/cbor: Prototype poisoning via `__proto__` map keys in CBOR decoding
IDs: CVE-2026-106448, GHSA-w48f-fwg7-ww6p
Record: https://patchnext.com/advisories/cve-2026-106448 (revision 3, source checked 26 Oct 2026, 12:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @stablelib/cbor 2.0.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @stablelib/cbor: affected < 2.0.3; fixed in 2.0.3

## Suggested inspection (read-only)
- `npm ls @stablelib/cbor --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 @stablelib/cbor.
- 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-w48f-fwg7-ww6p (OSV record GHSA-w48f-fwg7-ww6p lists affected ranges: npm @stablelib/cbor >=0 <2.0.3 (fixed))
- Verified: https://github.com/advisories/GHSA-w48f-fwg7-ww6p (GitHub-reviewed advisory GHSA-w48f-fwg7-ww6p lists affected ranges: npm @stablelib/cbor >=0 <2.0.3)

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