CVE-2025-4035 in libsoup
Summary
by MITRE • 04/29/2025
A flaw was found in libsoup. When handling cookies, libsoup clients mistakenly allow cookies to be set for public suffix domains if the domain contains at least two components and includes an uppercase character. This bypasses public suffix protections and could allow a malicious website to set cookies for domains it does not own, potentially leading to integrity issues such as session fixation.
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Analysis
by VulDB Data Team • 11/18/2025
The vulnerability identified as CVE-2025-4035 resides within the libsoup library, a widely-used HTTP client library for applications built on the glib platform ecosystem. This flaw represents a critical breach in cookie handling mechanisms that directly impacts web application security and user privacy. The vulnerability specifically affects how libsoup processes cookie domain attributes when they contain uppercase characters and consist of multiple domain components, creating a pathway for improper cookie setting that undermines fundamental web security practices.
The technical implementation of this vulnerability stems from libsoup's insufficient validation of cookie domain attributes during the cookie setting process. When a cookie domain contains at least two components and includes uppercase characters, the library fails to properly enforce the public suffix list restrictions that are standard practice in web browsers and security frameworks. This occurs because the library does not perform case-insensitive comparison against the public suffix list or does not properly validate that the domain component falls within the appropriate scope for cookie setting. The flaw essentially allows a malicious actor to bypass the standard protections that prevent cookies from being set on public suffix domains such as .com, .org, or .net, which are domains that should not be accessible to individual websites for cookie management purposes.
The operational impact of this vulnerability extends beyond simple session management issues to encompass broader security implications that could compromise user sessions and enable sophisticated attacks. An attacker could exploit this vulnerability by crafting cookie domain attributes that contain uppercase characters and multiple components, thereby allowing them to set cookies on domains that they do not own. This creates opportunities for session fixation attacks where an attacker can manipulate user sessions, potentially leading to unauthorized access to user accounts and sensitive information. The vulnerability is particularly concerning because it operates silently in the background, allowing malicious cookies to be set without detection, and could enable cross-site tracking, credential theft, and other session-based attacks that are typically prevented by proper cookie handling mechanisms.
Mitigation strategies for CVE-2025-4035 must address both immediate remediation and long-term architectural improvements to prevent similar vulnerabilities. Organizations should prioritize updating to the latest version of libsoup that contains the patched cookie handling logic, ensuring that domain validation properly enforces public suffix restrictions regardless of character case. Additionally, security teams should implement comprehensive monitoring of cookie-setting activities within their applications to detect anomalous patterns that might indicate exploitation attempts. The fix should align with established security standards such as those outlined in CWE-384, which addresses session management flaws, and should be consistent with ATT&CK framework techniques related to credential access and session hijacking. Network security controls should also be enhanced to detect and prevent suspicious cookie-related traffic patterns, while application developers should conduct thorough code reviews focusing on cookie handling components to identify potential similar vulnerabilities in custom implementations.