CVE-2026-1761: libsoup Buffer Overflow Vulnerability

CVE-2026-1761 Overview

A stack-based buffer overflow vulnerability has been identified in libsoup, a widely-used HTTP client/server library for GNOME. This critical flaw occurs during the parsing of multipart HTTP responses due to an incorrect length calculation in the boundary processing logic. Remote attackers can exploit this vulnerability by sending specially crafted multipart HTTP responses to applications using the affected library, potentially leading to memory corruption, application crashes, or arbitrary code execution.

The vulnerability is particularly concerning because it does not require authentication or user interaction to exploit, making it accessible to any network-based attacker who can send malicious HTTP responses to vulnerable applications.

Critical Impact

Remote attackers can achieve arbitrary code execution without authentication by exploiting a stack-based buffer overflow in libsoup's multipart HTTP response parser, affecting any application that processes untrusted server responses.

Affected Products

• libsoup (HTTP client/server library)
• GNOME-based applications using libsoup for HTTP communication
• Red Hat Enterprise Linux distributions with vulnerable libsoup packages

Discovery Timeline

• 2026-02-02 - CVE-2026-1761 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-1761

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when data is written beyond the boundaries of a stack-allocated buffer. In the context of libsoup, the vulnerability manifests during the processing of multipart HTTP responses, which are commonly used for file uploads, streaming data, and multi-part form submissions.

The flaw stems from an incorrect length calculation when parsing multipart boundaries. When libsoup receives a multipart HTTP response, it must identify and process the boundary markers that separate different parts of the response. Due to a calculation error in the boundary length handling, an attacker can craft a response that causes the library to write more data to the stack buffer than allocated, corrupting adjacent memory.

Applications that process untrusted server responses—such as web browsers, HTTP clients, and API consumers—are particularly vulnerable. The exploitation does not require any form of authentication or user interaction, significantly lowering the barrier for attack.

Root Cause

The root cause of CVE-2026-1761 is an incorrect length calculation in the multipart HTTP response parsing code within libsoup. When processing boundary markers in multipart responses, the library fails to properly validate the relationship between the declared content length and the actual buffer size allocated on the stack. This miscalculation allows data to overflow the intended buffer boundaries, leading to stack corruption.

Stack-based buffer overflows are particularly dangerous because they can overwrite return addresses, function pointers, and other control data stored on the stack, enabling attackers to redirect program execution to malicious code.

Attack Vector

The attack vector is network-based and can be executed remotely. An attacker must be able to send HTTP responses to a victim application—either by compromising an upstream server, performing a man-in-the-middle attack, or tricking the application into connecting to a malicious server.

The attack scenario involves sending a specially crafted multipart HTTP response with manipulated boundary markers and length values. When the vulnerable libsoup library parses this response, the incorrect length calculation causes a stack buffer overflow. The attacker can carefully construct the overflow data to overwrite the return address on the stack, redirecting execution to attacker-controlled shellcode or ROP gadgets.

Since no authentication or user interaction is required, this vulnerability represents a significant risk for any application that may receive HTTP responses from untrusted or compromised servers.

Detection Methods for CVE-2026-1761

Indicators of Compromise

• Unexpected application crashes in processes using libsoup, particularly during HTTP response processing
• Stack canary violation warnings or SIGABRT signals indicating stack corruption
• Unusual network traffic patterns with malformed multipart HTTP responses containing abnormal boundary lengths
• Memory corruption artifacts in application crash dumps related to HTTP parsing functions

Detection Strategies

• Monitor system logs for application crashes associated with libsoup or HTTP response processing
• Deploy network intrusion detection rules to identify malformed multipart HTTP responses with suspicious boundary values
• Use memory protection mechanisms (ASLR, stack canaries, DEP/NX) to detect and prevent exploitation attempts
• Implement application-level logging for HTTP response parsing errors and boundary validation failures

Monitoring Recommendations

• Enable crash reporting for applications that utilize libsoup to identify potential exploitation attempts
• Configure network security appliances to inspect HTTP traffic for anomalous multipart response structures
• Review system audit logs for signs of unexpected process behavior following HTTP communications
• Deploy endpoint detection solutions capable of identifying memory corruption exploitation techniques

How to Mitigate CVE-2026-1761

Immediate Actions Required

• Update libsoup packages to the latest patched versions provided by your distribution vendor
• Review and audit applications that process untrusted HTTP responses for exposure to this vulnerability
• Consider network segmentation to limit exposure of vulnerable systems to untrusted HTTP traffic
• Enable memory protection mechanisms (ASLR, stack canaries, NX bit) on systems running vulnerable applications

Patch Information

Multiple security advisories have been released addressing this vulnerability:

• Red Hat Security Advisory RHSA-2026:1948
• Red Hat Security Advisory RHSA-2026:2005
• Red Hat Security Advisory RHSA-2026:2006
• Red Hat Security Advisory RHSA-2026:2007
• Red Hat Security Advisory RHSA-2026:2008
• Red Hat Security Advisory RHSA-2026:2049
• Red Hat Security Advisory RHSA-2026:2182

For additional technical details, refer to the Red Hat CVE Analysis for CVE-2026-1761 and Red Hat Bug Report #2435961.

Workarounds

• Restrict applications from connecting to untrusted HTTP servers where possible
• Implement a reverse proxy or WAF to inspect and sanitize multipart HTTP responses before they reach vulnerable applications
• Use network-level controls to limit which servers can send HTTP responses to vulnerable systems
• Consider containerization or sandboxing for applications that must process untrusted HTTP content

# Update libsoup on Red Hat-based systems
sudo dnf update libsoup libsoup3

# Verify installed version after patching
rpm -qa | grep libsoup