CVE-2026-102559 in Red Hat
Summary
by MITRE • 09/29/2026
A flaw was found in libsoup. When constructing a masked WebSocket client frame for a very large outgoing payload, size values passed to GByteArray allocation APIs could be truncated while the masking routine still used the full length, causing a heap buffer overflow.
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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 rooted in improper handling of data sizes during WebSocket frame construction. Specifically, when processing outgoing payloads that exceed certain size thresholds, the application fails to correctly manage integer boundaries before allocating memory buffers. This flaw manifests as a heap buffer overflow, which occurs because the system allocates a smaller amount of memory than required based on truncated size values, while subsequent operations attempt to write data using the full, untruncated length. Such discrepancies between allocated and used sizes are classic indicators of CWE-190 Integer Overflow or Wraparound leading to CWE-122 Heap-based Buffer Overflow. The root cause lies in the failure to validate that the calculated buffer size accurately reflects the actual payload dimensions before invoking GByteArray allocation APIs, a common pitfall in C/C++ applications where implicit type conversions can silently truncate large integers into smaller data types without raising exceptions or errors.
From an operational perspective, this vulnerability allows for potential remote code execution if an attacker can control the content of the outgoing WebSocket message and trigger the specific conditions that lead to truncation. Although the description notes it is a masked client frame, meaning the application itself initiates the connection, the impact remains severe because heap buffer overflows provide attackers with arbitrary read and write capabilities in memory. This capability enables the corruption of adjacent data structures, such as function return addresses or object pointers, which can be leveraged to hijack control flow. In enterprise environments where libsoup is utilized for HTTP and WebSocket communications, particularly within GNOME-based applications or backend services relying on this library, exploitation could lead to complete system compromise. The severity is further amplified by the fact that heap overflows are often more difficult to detect than stack overflows due to their asynchronous nature and the complexity of memory management in modern operating systems.
The technical mechanics involve a mismatch between the size parameter passed to the allocation function and the length used during the masking routine. When constructing WebSocket frames, data must be masked according to RFC 6455 standards. If the library truncates the payload size before allocating the buffer but proceeds to mask the entire original payload, it writes beyond the bounds of the allocated heap region. This out-of-bounds write corrupts memory metadata or adjacent objects on the heap. Attackers may exploit this by crafting payloads that trigger specific allocation patterns, allowing them to place malicious data in predictable locations relative to the overflowed buffer. The lack of rigorous boundary checks before arithmetic operations is a fundamental design flaw that violates secure coding principles emphasized in standards like CWE-131 Incorrect Calculation of Buffer Size and CWE-682 Incorrect Conversion between Numeric Types.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary solution involves updating libsoup to versions where this integer truncation issue has been patched, ensuring that size calculations are performed using appropriate data types such as uint32_t or larger without implicit narrowing conversions. Developers should implement explicit checks to verify that the calculated buffer size does not exceed maximum allowable limits before allocation. Additionally, enabling compiler-based security features like AddressSanitizer during development and testing phases can help detect such memory errors early in the lifecycle. For organizations relying on this library, it is crucial to monitor for updates from upstream maintainers and apply patches promptly. Furthermore, adopting static analysis tools that specifically look for integer overflow patterns and buffer size mismatches can prevent similar vulnerabilities from being introduced into related codebases. The ATT&CK framework categorizes such exploitation under T1203 Exploitation for Client Execution or potentially T1059 Command and Scripting Interpreter if the overflow leads to script injection, highlighting the need for robust input validation and memory-safe programming practices across all network-facing components.