CVE-2026-5857

Contiki-NG's MQTT client parse_publish_vhdr() in os/net/app-layer/mqtt/mqtt.c sets topic_len_received=1 before checking topic_len against the 64-byte limit, so an over-length topic returns early but leaves the flag set. On the next TCP segment, tcp_input() re-invokes the parser with topic_received==0, and the persisted topic_len_received==1 skips the length-reading block containing the guard, falling through directly to a memcpy() that uses the unvalidated 16-bit topic_len as the copy length. The 65-byte topic[] destination overruns into adjacent struct fields including the payload_chunk pointer, which subsequent MQTT code dereferences, giving a compromised or attacker-controlled broker an arbitrary-pointer-write primitive. Contiki-NG's MQTT implementation has no TLS support so the connection is plaintext. Impact ranges from information disclosure and denial of service to remote code execution on embedded targets without memory protection.

CVSS v3 8.1 HIGH

8.1^/10

CVSS v3 : HIGH

Vector :

Exploitability : 2.2 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/contiki-ng/contiki-ng
https://github.com/contiki-ng/contiki-ng/commit/a34a2dbdc8bea784bd2ae5079aa4be520cd74f2d
https://github.com/contiki-ng/contiki-ng/pull/3163
https://y637f9qq2x.com/posts/cve-2026-5857/

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-06 22:18

Updated : 2026-08-13 21:18

NVD link : CVE-2026-5857

Mitre link : CVE-2026-5857

CVE.ORG link : CVE-2026-5857

JSON object : View

Products Affected

No product.

CWE

CWE-787

Out-of-bounds Write

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