---
id: "CVE-2026-129114"
page: "https://infrastack.ai/live/CVE-2026-129114"
kind: "vulnerability"
aliases: ["CVE-2026-129114"]
title: "JSON::XS for Perl: one-byte heap overflow when parsing streamed JSON"
severity: "medium"
cvss: null
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["json-xs", "package", "perl"]
not_affected_if: ["not-incremental-parsing", "versions-outside-range"]
published_at: "2026-11-14T12:17:44+00:00"
first_seen_at: "2026-11-14T12:28:31+00:00"
updated_at: "2026-11-14T12:30:35+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-129114", "first_seen_at": "2026-11-14T12:28:31+00:00"}]
exploit_sources: []
---

# JSON::XS for Perl: one-byte heap overflow when parsing streamed JSON

Link for people: https://infrastack.ai/live/CVE-2026-129114 (this .md is for agents)

JSON::XS, a Perl module for encoding and decoding JSON, writes one NUL byte past a heap buffer when incremental parsing appends a one-byte chunk. A peer that controls how its JSON is split into reads can use this to corrupt memory in the consuming process.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `perl -MJSON::XS -e 'print $JSON::XS::VERSION'` and compare the output against the affected range 3.04 to before 4.05.
- Search dependency manifests and lockfiles for `JSON::XS` and any Perl application that calls `incr_parse`.

## Fix

- JSON::XS `4.05` or later (fixed version per the affected range before 4.05).

## Timeline

- 2026-11-14T12:28:31+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-129114

## From the sources

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.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_