# CVE-2026-124541: JSON::XS versions before 4.05 for Perl leak the decoded part of a rejected long string in decode_str

Status: published. Published: 2026-11-14. Updated: 2026-11-14.

JSON::XS versions before 4.05 for Perl leak the decoded part of a rejected long string in decode_str.

A string is decoded through a fixed-size buffer (16 KiB in 4.04), and each time the buffer fills its contents move into a new scalar. Nothing frees that scalar when the string is then rejected for a control character, an invalid escape, malformed UTF-8 or the end of the input.

A process that keeps running after a failed decode retains the decoded part of each rejected string, with its size chosen by the sender. Repeated requests exhaust process memory.

## Remediation

- fix: Upgrade to JSON-XS 4.05 or later. (source: CNA: CPANSec)

## Affected products and versions

-  /  (JSON-XS): ≥ 0; < 4.05 (affected, custom). Source: CNA: CPANSec

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-401

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://metacpan.org/release/MLEHMANN/JSON-XS-4.05/changes (CNA: CPANSec; release-notes)

## Provenance

- CNA: CPANSec: https://www.cve.org/CVERecord?id=CVE-2026-124541; retrieved 2026-11-14; source updated 2026-11-14

Revision: cbcb7459b232768a60bb8ebaaf2e24d102537b9e390d3713e11ab419e6f4275f

Canonical: https://y2.dev/cve/CVE-2026-124541

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