Remote code execution via persistent MQTT parser state
Published Aug 6, 2026 · Updated Aug 6, 2026
Out-of-bounds write in Contiki-NG's MQTT PUBLISH parser allows remote attackers to execute code via a split broker response. The parse_publish_vhdr() function sets topic_len_received before rejecting an oversized topic; the next TCP segment then skips that guard and copies the unvalidated 16-bit length into the 65-byte topic buffer. Exploitation requires control of the configured broker or a man-in-the-middle position on the plaintext MQTT connection, and it can disclose memory, interrupt the device, or redirect execution on targets without memory protection.
Summary
What happened
Out-of-bounds write in Contiki-NG's MQTT PUBLISH parser allows remote attackers to execute code via a split broker response. The parse_publish_vhdr() function sets topic_len_received before rejecting an oversized topic; the next TCP segment then skips that guard and copies the unvalidated 16-bit length into the 65-byte topic buffer. Exploitation requires control of the configured broker or a man-in-the-middle position on the plaintext MQTT connection, and it can disclose memory, interrupt the device, or redirect execution on targets without memory protection.
The record
- CVE
- CVE-2026-5857
- Published
- Aug 6, 2026
- Updated
- Aug 6, 2026
- Vendor
- Contiki-NG
- Product
- Contiki-NG
- Classifications
- CWE-787, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 6, 2026CVE publishedPublication date reported by the CVE source.
- Aug 6, 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?
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- Affected versionversion=0 <a34a2dbdc8bea784bd2ae5079aa4be520cd74f2d
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
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.
Public exploit references
- Malicious MQTT broker proof of conceptfunctional · demonstrated
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Technologies
Your stack
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Your stack
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