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Medium, CVSS 6.2amended

stream-json: FlexAssembler string/RegExp path filters join the full key stack per container start, giving O(depth^2) CPU denial of service

CVE-2026-114129GHSA-jj87-hc4r-jwfw

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (stream-json 3.7.0), 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

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.2 · CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-114129: 0.25% estimated exploitation activity in the next 30 days; percentile 17.11 (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 FlexAssembler, the custom-container assembler shipped in the stream-json package (src/core/utils/flex-assembler.js, re-exported at stream-json/utils/flex-assembler.js and stream-json/web/utils/flex-assembler.js), compiles a string or RegExp path filter into a matcher that runs keyStack.join(separator) on every container start. Because the key stack grows one entry per open object or array with no depth bound, a JSON document nested to depth D drives D container-start tokens that each perform an O(D) join, for O(D^2) total CPU on the single-threaded event loop. An unauthenticated party who can supply JSON bytes to a pipeline that uses a FlexAssembler with a string or RegExp rule filter can stall the process with a small input: roughly 96 KB (depth 16000) blocks the event loop for over a second, and the cost grows quadratically. Root Cause FlexAssembler reconstructs JavaScript values from the parser token stream and supports custom containers selected by path-matching rules.…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-jj87-hc4r-jwfw

  2. Revision 2 · amended ·

    Amended from osv record GHSA-jj87-hc4r-jwfw

  3. Revision 1 · created ·

    Published from ghsa record GHSA-jj87-hc4r-jwfw

Agent brief

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# Patch Next advisory brief: CVE-2026-114129

Advisory: stream-json: FlexAssembler string/RegExp path filters join the full key stack per container start, giving O(depth^2) CPU denial of service
IDs: CVE-2026-114129, GHSA-jj87-hc4r-jwfw
Record: https://patchnext.com/advisories/cve-2026-114129 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: stream-json 3.7.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm stream-json: affected >= 2.0.0, <= 3.6.0; fixed in 3.7.0

## Suggested inspection (read-only)
- `npm ls stream-json --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 stream-json.
- 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-jj87-hc4r-jwfw (GitHub-reviewed advisory GHSA-jj87-hc4r-jwfw lists affected ranges: npm stream-json >=2.0.0 <=3.6.0)
- Verified: https://osv.dev/vulnerability/GHSA-jj87-hc4r-jwfw (OSV record GHSA-jj87-hc4r-jwfw lists affected ranges: npm stream-json >=2.0.0 <3.7.0 (fixed))

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