Application crash via unchecked trailing-whitespace lookahead
Published Sep 8, 2026 · Updated Sep 8, 2026
Out-of-bounds read in the mJS lexer through 1.26 allows remote attackers to crash instrumented embedding applications via crafted JavaScript. The skip_spaces_and_comments function advances past trailing whitespace to the null terminator, then reads p->pos[1] without first confirming input remains. Any embedding application that passes untrusted JavaScript ending in whitespace reaches the lexer path; reported impact is an AddressSanitizer-detected crash, not a write or code execution.
Summary
What happened
Out-of-bounds read in the mJS lexer through 1.26 allows remote attackers to crash instrumented embedding applications via crafted JavaScript. The skip_spaces_and_comments function advances past trailing whitespace to the null terminator, then reads p->pos[1] without first confirming input remains. Any embedding application that passes untrusted JavaScript ending in whitespace reaches the lexer path; reported impact is an AddressSanitizer-detected crash, not a write or code execution.
The record
- CVE
- CVE-2026-86716
- Published
- Sep 8, 2026
- Updated
- Sep 8, 2026
- Vendor
- Cesanta
- Product
- mJS
- Classifications
- CWE-122, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 8, 2026CVE publishedPublication date reported by the CVE source.
- Sep 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=1.0
- Affected versionversion=1.1
- Affected versionversion=1.10
- Affected versionversion=1.11
- Affected versionversion=1.12
- Affected versionversion=1.13
- Affected versionversion=1.14
- Affected versionversion=1.15
- Affected versionversion=1.16
- Affected versionversion=1.17
- Affected versionversion=1.18
- Affected versionversion=1.19
- Affected versionversion=1.2
- Affected versionversion=1.20
- Affected versionversion=1.21
- Affected versionversion=1.22
- Affected versionversion=1.23
- Affected versionversion=1.24
- Affected versionversion=1.25
- Affected versionversion=1.26
- Affected versionversion=1.3
- Affected versionversion=1.4
- Affected versionversion=1.5
- Affected versionversion=1.6
- Affected versionversion=1.7
- Affected versionversion=1.8
- Affected versionversion=1.9
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- mjs_exec trailing-whitespace proof of conceptfunctional · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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