CVE-2026-119053 in lwIP
Summary
by MITRE • 10/29/2026
lwIP 2.0.0 through 2.2.1 built with the SNMP agent contains an out-of-bounds read vulnerability in snmp_pbuf_stream_writeto() that bounds copies by pbuf->len instead of remaining bytes. Remote unauthenticated attackers knowing the read community can send fragmented SNMP requests to receive adjacent receive-buffer or pool memory echoed in responses.
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Analysis
by VulDB Data Team • 10/29/2026
The vulnerability identified within lwIP versions 2.0.0 through 2.2.1, specifically when compiled with the Simple Network Management Protocol agent enabled, represents a critical out-of-bounds read flaw located in the snmp_pbuf_stream_writeto function. This component is responsible for handling data streams during SNMP operations, and its failure to correctly validate buffer boundaries allows an attacker to access memory regions that are not intended for exposure. The core technical defect stems from an incorrect boundary check mechanism where the copy operation is limited by the total length of the pbuf structure rather than calculating the remaining bytes available within the current stream context. This logical error means that when data is being written or read, the function does not account for how much data has already been processed in previous fragments, leading to a situation where subsequent reads can extend beyond the intended buffer limits into adjacent memory spaces.
From an operational perspective, this vulnerability enables remote unauthenticated attackers who possess knowledge of the SNMP read community string to exploit the flaw by sending specially crafted fragmented SNMP requests. Because lwIP processes these packets incrementally due to fragmentation, the miscalculation in byte counting accumulates across fragments, eventually allowing the application to read from memory locations outside the allocated buffer. The immediate impact is the leakage of sensitive information contained within adjacent receive-buffer or pool memory. This data echo back in SNMP responses can include internal state variables, network configuration details, stack pointers, or other proprietary information that aids further exploitation attempts against the target device. Such leaks are particularly dangerous in embedded systems and IoT devices where lwIP is commonly deployed, as they provide attackers with valuable intelligence for crafting more sophisticated attacks.
This vulnerability aligns closely with CWE-125, which describes an out-of-bounds read condition resulting from improper validation of input boundaries during memory access operations. The exploitation technique leverages the fragmented nature of network packets to bypass initial sanity checks that might otherwise prevent a single large request from causing harm. By splitting malicious payloads across multiple smaller packets, the attacker manipulates the internal state tracking mechanisms of the SNMP agent, effectively tricking it into believing there is more valid data available than actually exists within the current buffer segment. This approach exploits the cumulative nature of stream processing without triggering immediate error conditions that would abort the connection or request.
In terms of threat modeling and adversary behavior, this vulnerability maps to techniques found in the MITRE ATT&CK framework under Information Discovery, specifically Data from Network Shared Drive or potentially Remote Services depending on the specific implementation context. The ability to read arbitrary memory via a network service constitutes a significant breach of confidentiality principles defined by industry standards such as ISO/IEC 27001. Attackers can use this information leakage to map out the internal architecture of the target system, identify running services, or locate credentials stored in nearby memory pools. This facilitates lateral movement and privilege escalation scenarios where initial access is gained through SNMP but leads to deeper compromise of the host operating system or application layer.
Mitigation strategies must prioritize updating lwIP to a version that corrects the boundary calculation logic within snmp_pbuf_stream_writeto(). Developers should ensure that the remaining byte count is accurately tracked and enforced during every fragment processing step, ensuring that no read operation exceeds the allocated buffer size regardless of fragmentation patterns. Additionally, organizations relying on SNMP for network management should consider disabling unnecessary services if not required, implementing strict access control lists to restrict SNMP traffic to trusted subnets only, and employing intrusion detection systems capable of identifying anomalous fragmented packet sequences targeting managed devices. Regular security audits focusing on embedded protocol implementations are essential to prevent similar logic errors in other network stack components that may share analogous architectural patterns.