| Title | lwIP Project lwIP 2.2.1 and earlier Heap-based Buffer Overflow |
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| Description | A heap-based out-of-bounds write exists in the lwIP MQTT client. In mqtt_parse_incoming(), the MQTT Remaining Length field is parsed without enforcing the protocol limit of four encoded bytes. A broker can send a malformed Remaining Length containing excessive continuation bytes, causing msg_idx to advance beyond the fixed rx_buffer and overwrite adjacent heap memory.
The issue was reproduced with AddressSanitizer using a crafted MQTT input. The lwIP maintainer confirmed the issue and marked Savannah bug #68590 as fixed, with the fix planned for lwIP 2.2.2. |
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| Source | ⚠️ https://savannah.nongnu.org/bugs/?68590 |
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| User | xuyun (UID 100919) |
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| Submission | 09/01/2026 04:48 (2 months ago) |
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| Moderation | 10/10/2026 17:18 (1 month later) |
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| Status | Duplicate |
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| VulDB entry | 408720 [lwIP up to 2.2.1 MQTT out-of-bounds write] |
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| Points | 0 |
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