Heap-based Buffer Overflow in Cesanta mJS Affects Multiple Versions
CVE-2026-86716

6.9MEDIUM

Key Information:

Vendor

Cesanta

Status
Mjs
Vendor
CVE Published:
8 September 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-86716?

A vulnerability has been identified in Cesanta mJS up to version 1.26, specifically within the 'skip_spaces_and_comments' function in src/mjs_tok.c. This issue allows for a heap-based buffer overflow, which can be exploited remotely. The vulnerability has been publicly disclosed, and potential attackers may leverage this exploit. Despite being notified early via an issue report, the project maintainers have yet to respond or release a patch.

Affected Version(s)

mJS 1.0

mJS 1.1

mJS 1.2

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-86716 - Proof of Concept

References

https://vuldb.com/vuln/399773
vdb-entrytechnical-description
https://vuldb.com/vuln/399773/cti
signaturepermissions-required
https://vuldb.com/cve/CVE-2026-86716
third-party-advisory

CVSS V4

Score:
6.9
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

lrrh (VulDB User)
VulDB CNA Team
.