CVE-2026-102558 in Red Hat
Summary
by MITRE • 09/29/2026
A flaw was found in libsoup. When max-incoming-payload-size is unlimited (0), SoupWebsocketConnection could grow its incoming GByteArray based on an attacker-controlled frame length until the length wrapped, causing a heap buffer overflow while reading frame data.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified within the libsoup library represents a critical memory safety issue affecting WebSocket connections managed by the SoupWebsocketConnection component. This flaw stems from improper validation of input size parameters when handling incoming network frames. Specifically, the configuration parameter max-incoming-payload-size allows administrators or developers to set an upper limit on the size of data payloads accepted during communication sessions. When this value is explicitly configured to zero, it signals that there is no maximum limit imposed on incoming payload sizes, effectively allowing unlimited growth of internal buffers designed to accumulate frame data.
The technical root cause lies in how the library manages memory allocation for these dynamic byte arrays. As an attacker controls the length field within WebSocket frames sent to the vulnerable service, they can dictate the amount of memory allocated via GByteArray expansion mechanisms. The critical failure occurs when this controlled length value approaches or exceeds the maximum capacity of a signed integer type used internally by the system. Due to standard arithmetic behavior in many programming environments, adding large values can result in an integer overflow where the calculated size wraps around from a very large positive number to a small negative or near-zero positive number. Consequently, the memory allocator reserves only a minimal amount of heap space based on this wrapped value, while subsequent operations attempt to write frame data corresponding to the original, much larger intended length into that insufficiently sized buffer.
This discrepancy between allocated and expected sizes leads directly to a heap-based buffer overflow condition. During the process of reading and storing incoming frame data, the application writes beyond the boundaries of the allocated memory region. This out-of-bounds write operation corrupts adjacent memory structures on the heap, which can include metadata used by the allocator or other critical program variables. Such corruption is particularly dangerous because it provides an attacker with a mechanism to manipulate control flow within the process. By carefully crafting the overflow payload, an adversary may overwrite function pointers or return addresses stored in nearby memory locations, potentially achieving arbitrary code execution on the affected system.
From an operational perspective, this vulnerability poses severe risks to any service relying on libsoup for WebSocket communications that permits unlimited incoming payloads. Attackers can exploit this flaw remotely by establishing a connection and sending specially crafted frames with large length fields. The exploitation does not necessarily require authentication if the endpoint is publicly accessible or if valid credentials are obtained through other means. Successful exploitation could result in complete compromise of the host system, including data exfiltration, installation of persistent backdoors, or denial of service conditions caused by application crashes due to memory corruption detection mechanisms like ASLR or heap sanitizers triggering on invalid access patterns.
This issue aligns with Common Weakness Enumeration category CWE-190, which describes integer overflow or wraparound errors that lead to subsequent vulnerabilities such as buffer overflows. It also maps to MITRE ATT&CK technique T1203, specifically the exploitation of client-side software for initial access and execution. The vulnerability highlights the importance of strict input validation and size checking in network-facing components, particularly when dealing with variable-length data structures like WebSocket frames where length fields are directly influenced by external inputs.
Mitigation strategies must focus on enforcing reasonable limits on incoming payload sizes regardless of configuration defaults that might allow unlimited growth. Developers should ensure that max-incoming-payload-size is set to a positive integer value appropriate for the application's operational requirements, thereby preventing the allocation logic from entering states where large values could wrap around. Additionally, implementing defensive programming practices such as checking for potential overflows before performing arithmetic operations on size variables can prevent this class of errors. Upgrading to patched versions of libsoup that include fixes for this specific integer handling issue is essential for restoring security posture in affected environments. Regular auditing of network library configurations and continuous integration testing with fuzzing tools targeting WebSocket implementations can further reduce the risk of similar vulnerabilities going undetected in production systems.