CVE-2026-66337 in Red Hat
Summary
by MITRE • 07/25/2026
A flaw was found in libsoup. An unsigned integer underflow in the soup_filter_input_stream_read_until() function causes a heap buffer over-read when parsing multipart HTTP responses. A malicious HTTP server can exploit this by sending a crafted multipart response, potentially causing the client application to crash or disclose sensitive heap memory.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability exists within the libsoup library, a widely-used HTTP client library for applications built on the glib framework and commonly employed in desktop environments and networked applications. This flaw manifests as an unsigned integer underflow within the soup_filter_input_stream_read_until() function, which is responsible for parsing multipart HTTP responses. The issue arises when processing malformed multipart data where the underlying logic fails to properly validate boundary conditions during buffer management operations.
The technical implementation of this vulnerability involves a specific arithmetic operation where an unsigned integer variable becomes insufficiently bounded during processing of HTTP response boundaries. When the soup_filter_input_stream_read_until() function encounters a crafted multipart response from a malicious server, the underflow condition causes subsequent memory access operations to reference invalid memory locations. This leads to a heap buffer over-read scenario where the application attempts to read beyond allocated memory boundaries, potentially accessing adjacent heap regions containing sensitive data.
From an operational perspective, this vulnerability presents significant risk to applications that utilize libsoup for HTTP communication, particularly those handling untrusted network responses without proper input validation. The exploitability requires a malicious HTTP server capable of crafting specific multipart responses that trigger the underflow condition, but once triggered, the impact can range from application crashes to potential information disclosure. Attackers could leverage this vulnerability to cause denial-of-service conditions or gain access to sensitive heap memory contents that might include authentication tokens, personal data, or other confidential information.
The vulnerability aligns with CWE-190, which addresses integer overflow and underflow conditions, specifically focusing on unsigned integer underflows that can lead to memory corruption. From an attack framework perspective, this issue maps to the ATT&CK technique T1211 for exploitation of known vulnerabilities in common libraries. The impact extends beyond immediate application stability concerns to potential data leakage scenarios, particularly affecting applications running with elevated privileges or those handling sensitive user information.
Mitigation strategies should prioritize updating to patched versions of libsoup where the integer underflow has been corrected through proper boundary validation and input sanitization. Additionally, implementing network-level filtering to restrict access to potentially malicious HTTP servers can provide defense-in-depth measures. Applications utilizing libsoup should also implement robust error handling around HTTP response parsing operations and consider employing memory safety techniques such as address sanitizers during development testing phases to detect similar vulnerabilities in other components of the application stack.