# CVE-2026-129114: JSON::XS versions from 3.04 before 4.05 for Perl write one byte past a heap buffer when appending a one-byte chunk in incr_parse

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

JSON::XS versions from 3.04 before 4.05 for Perl write one byte past a heap buffer when appending a one-byte chunk in incr_parse.

The incremental buffer grows to one and a half times the length it must hold, with no room reserved for the terminating NUL. For an empty buffer and a one-byte chunk that request is one byte, which a buffer whose front was removed by earlier decodes can already have, so nothing is reallocated and the NUL lands one byte past the allocation.

A peer streaming data to an incr_parse consumer, choosing how the input is split into reads, can cause a one-byte heap out-of-bounds write.

## Remediation

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

## Affected products and versions

-  /  (JSON-XS): ≥ 3.04; < 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-193, CWE-122

## 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-2026-129114; retrieved 2026-11-14; source updated 2026-11-14

Revision: c3ca15105cd0ee2b3fbeaa6a771a078c5d035b770370e8540bd11555b19c07d2

Canonical: https://y2.dev/cve/CVE-2026-129114

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