CVE-2026-102557 in Red Hat
Summary
by MITRE • 09/29/2026
A flaw was found in libsoup. When reassembling fragmented WebSocket messages into a GByteArray, libsoup did not adequately cap total message size against the limits of the underlying buffer type. A remote peer could send fragments that caused size truncation while the implementation still used the full length, leading to heap corruption or a crash.
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Analysis
by VulDB Data Team • 09/29/2026
The vulnerability identified in libsoup represents a critical memory safety issue within the library's WebSocket message reassembly logic. Libsoup is widely utilized as a core HTTP and networking client library for many prominent Linux desktop environments and applications, including GNOME-based software such as Epiphany web browser and Evolution email client. The specific flaw occurs during the process of reconstructing fragmented WebSocket frames into a single contiguous data structure known as GByteArray. In network protocols like WebSocket, messages are often split into multiple smaller frames to optimize transmission efficiency or adhere to buffer size constraints on either end of the connection. When libsoup receives these fragments, it must aggregate them back together before passing the complete message up to the application layer for processing.
The technical root cause lies in an inadequate validation check regarding total message size relative to the capacity limits of the underlying GByteArray implementation. Specifically, when accumulating fragment data, the library failed to properly cap or validate the cumulative length against integer overflow boundaries or maximum allocation sizes supported by the buffer type. This oversight allows a remote attacker who controls the WebSocket server endpoint to craft maliciously sized fragments that trigger size truncation during internal calculations while the application logic continues to operate under the assumption of a larger, valid message size. Consequently, subsequent memory operations based on this incorrect length value can write beyond the allocated heap boundaries or attempt allocations that exceed system limits, resulting in heap corruption.
The operational impact of this vulnerability is severe due to its potential for remote code execution and denial of service. Heap corruption typically leads to undefined behavior within the host application, which frequently manifests as a crash, thereby causing a Denial of Service condition against users interacting with affected services or applications. More critically, if an attacker can control the data written during this out-of-bounds memory access, they may achieve arbitrary code execution on the victim's machine. Given that libsoup is embedded in many user-facing desktop applications, exploitation could allow an adversary to compromise the integrity and confidentiality of sensitive user data stored locally or intercept network traffic processed by these applications. This risk is heightened because WebSocket connections are often established over persistent channels where a single malicious server can send multiple fragmented messages rapidly, increasing the attack surface for successful exploitation attempts.
From a classification perspective, this vulnerability aligns with CWE-120 Buffer Copy without Checking Size of Input and CWE-787 Out-of-bounds Write, as it involves writing data beyond allocated memory boundaries due to improper size validation. It also relates to CWE-697 Incorrect Comparison during Integer Conversion or Truncation if the truncation aspect is central to the bypass mechanism. In terms of adversary tactics, this flaw supports techniques associated with ATT&CK T1059 Command and Scripting Interpreter through potential code execution vectors, as well as T1427 Network Service Scanning for initial access via WebSocket endpoints that utilize libsoup.
Mitigation strategies should prioritize immediate updates to the latest stable version of libsoup where this size validation logic has been corrected. Developers integrating libsoup into custom applications must ensure their build environments are configured to pull these patched dependencies rather than relying on potentially outdated system libraries provided by older distribution packages. For organizations unable to patch immediately, network-level controls such as Web Application Firewalls can be deployed to inspect WebSocket traffic for unusually large or fragmented message patterns that deviate from expected protocol behavior. Additionally, enabling Address Sanitizer (ASan) during development and testing phases can help detect similar memory safety issues before they reach production environments. Security teams should also monitor for any exploit attempts targeting known vulnerable versions of libsoup through intrusion detection systems configured to flag anomalous WebSocket frame sizes or repeated connection resets indicative of crash-based denial-of-service attacks.