- Exploited
- No known exploitation
- Fix
- Fixed in 4.05
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 4.05.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 0/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
JSON::XS, a Perl JSON library, can be made to buffer incremental input without limit after a NUL byte, which can exhaust process memory. A peer streaming data to an incr_parse consumer can trigger this, regardless of the configured max_size.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Original description
JSON::XS versions before 4.05 for Perl allow memory exhaustion by buffering incremental input past max_size after a NUL byte in incr_parse.
The parser appends each chunk to its buffer and compares max_size with how far it has progressed, not with the buffer length. It treats a NUL byte as the end of the input, so a NUL within the first max_size bytes keeps it short of the limit. The buffer keeps growing, and incr_skip cannot remove the NUL.
A peer streaming data to an incr_parse consumer can exhaust process memory regardless of max_size.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure?/25Unknown. No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity?/10Unknown. No CVSS score or vendor rating
- No patch0/5No signal
What would change the score
- Would score about 55 if added to CISA KEV
- Would score about 50 if CISA's SSVC rates exploitation active
- Would score about 22 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 4.05.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-124536 (JSON::XS versions before 4.05 for Perl allow memory exhaustion by buffering incremental input past max_size after a NUL byte in incr_parse), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-124536 (entry last updated 2026-11-14):
Affected:
- JSON-XS: fixed in 4.05
Fixed versions: 4.05.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-124536 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-124536 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://metacpan.org/release/MLEHMANN/JSON-XS-4.05/changes
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-124536
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-124536"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- JSON-XS
fixed in 4.05
Evidence 3
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 1
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-124536
Is CVE-2026-124536 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-124536?
JSON-XS: before 4.05.Source: cve.now feed data
How do I fix CVE-2026-124536?
Upgrade to a fixed version: 4.05.Source: cve.now feed data