Serialize JavaScript: Cross-site scripting (XSS) via unescaped </script at the end of a serialized function body

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-115754: 0.23% estimated exploitation activity in the next 30 days; percentile 14.06 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
• CVE-2026-115897: 0.31% estimated exploitation activity in the next 30 days; percentile 23.54 (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.

Impact serialize-javascript escapes its output so it is safe to embed inside a <script element. Before 7.1.3 that guarantee did not hold for a function value whose source ends in a bare </script. Each function body is escaped on its own, and a bare </script was only neutralized when followed — within the same body — by a character the HTML tokenizer treats as ending the tag name (TAB, LF, FF, CR, SPACE, / or ). A body ending exactly at </script has no following character, so it was emitted unescaped. The delimiter is then supplied by the surrounding output (for example the newline the space option emits after the value), and a later serialized value can supply the closing followed by markup: Embedded in a <script element, the script ends at the injected tag and the <img becomes a live element in the page. Exploitation requires an attacker to control the source text of a serialized function, in practice through a spoofed toString(). Real functions always end in }, so ordinary function…

Published by the source

23 Oct 2026, 22:09 UTC

Last modified by the source

24 Oct 2026, 02:55 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 5 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m5mm-p8h7-m29v

2. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-m5mm-p8h7-m29v

3. Revision 3 · amended · 24 Oct 2026

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

4. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-m5mm-p8h7-m29v

5. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-m5mm-p8h7-m29v

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# Patch Next advisory brief: CVE-2026-115897

Advisory: Serialize JavaScript: Cross-site scripting (XSS) via unescaped </script at the end of a serialized function body
IDs: CVE-2026-115897, GHSA-m5mm-p8h7-m29v
Record: https://patchnext.com/advisories/cve-2026-115897 (revision 5, 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: Low (CVSS 2.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: serialize-javascript 7.1.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm serialize-javascript: affected < 7.1.3; fixed in 7.1.3

## Suggested inspection (read-only)
- `npm ls serialize-javascript --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 serialize-javascript.
- 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-m5mm-p8h7-m29v (GitHub-reviewed advisory GHSA-m5mm-p8h7-m29v lists affected ranges: npm serialize-javascript >=0 <7.1.3)
- Verified: https://osv.dev/vulnerability/GHSA-m5mm-p8h7-m29v (OSV record GHSA-m5mm-p8h7-m29v lists affected ranges: npm serialize-javascript >=0 <7.1.3 (fixed))

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