VulnerabilityPublished 14 Nov 2026

CVE-2026-129114: JSON-XS (Perl module) · Off-by-one Error

Affects JSON-XS (Perl module)Source CVE Database V5

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Not known to be exploited : upgrade to 4.05 soon.

Data as of 14 Nov 2026, 12:17 UTC

Severity

High

Rated High by Threat Radar's AI analysis · CVSS not yet scored by NVD

Thin evidence

One scorer or none

Patch: Available – fixed in 4.05

Exploitation evidence

Disclosed: evidence found.
CVE published 14 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 14 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade JSON-XS (Perl module) to 4.05.

Affected software

Product	Affected	Fixed in
JSON-XS	Affected >=3.04 <4.05	Fixed in 4.05
CPANJSON-XS`pkg:cpan/JSON-XS`Other threats	Affected >=3.04 <4.05	Fixed in 4.05

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade JSON::XS to version 4.05 or later, where this off-by-one heap buffer overflow is fixed. No other mitigation is indicated or required.

Description

JSON::XS versions from 3.04 up to but not including 4.05 for Perl contain an off-by-one error in the incr_parse function. This flaw causes the software to write one byte past the end of a heap buffer when appending a one-byte chunk during incremental parsing. The issue arises because the incremental buffer grows to one and a half times the required length without reserving space for the terminating NUL byte, leading to a heap out-of-bounds write under certain input conditions. The vulnerability is fixed in version 4.05.

Impact

This vulnerability can lead to a heap out-of-bounds write, which may cause memory corruption. While the exact impact is not detailed, such memory corruption could potentially be exploited to cause crashes or enable further attacks such as code execution or denial of service. No known exploits in the wild have been reported.

Summary

The vulnerability in JSON::XS (CVE-2026-129114) is an off-by-one heap buffer overflow caused by improper buffer size calculation in the incr_parse function. When appending a one-byte chunk, the incremental buffer does not reserve space for the terminating NUL byte, resulting in a one-byte write beyond the allocated heap buffer. This occurs specifically when the buffer front was removed by earlier decodes and no reallocation happens. A remote peer controlling the input stream can influence how data is split into reads, potentially triggering this out-of-bounds write. The issue affects versions >=3.04 and <4.05 and is fixed in 4.05.

CWE-193Off-by-one Error (opens in a new tab)
Base weakness
A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
Implementation
When copying character arrays or using character manipulation methods, the correct size parameter must be used to account for the null terminator that needs to be added at the end of the array.
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-122Heap-based Buffer Overflow (opens in a new tab)
Variant weaknessLikelihood of exploit: HighCWE Top 25 (2025): #16
The product writes past the end of a buffer that was allocated on the heap.
Pre-design: Use a language or compiler that performs automatic bounds checking.
Architecture and Design
Use an abstraction library to abstract away risky APIs. Not a complete solution.
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
Attack patterns
Forced Integer Overflow (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

metacpan.org/release/MLEHMANN/JSON-XS-4.05/changes (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 14 Nov 2026, 12:17 UTC

WeaknessesCWE-193, CWE-122

Technical details

References

Community reviews

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