CVE-2025-4969: libsoup Use-After-Free Vulnerability

CVE-2025-4969 Overview

CVE-2025-4969 is an out-of-bounds read vulnerability in the libsoup HTTP client and server library. The flaw stems from improper verification of multipart HTTP message termination. Attackers can send a crafted multipart HTTP body to a server that consumes libsoup, causing it to read beyond allocated memory boundaries. This exposes adjacent process memory contents and can crash the affected service.

The vulnerability is tracked under CWE-125: Out-of-bounds Read. It affects any application, daemon, or service that parses untrusted HTTP requests through libsoup, including desktop services on Linux distributions that depend on GNOME components.

Critical Impact
Remote attackers can trigger out-of-bounds memory reads over the network without authentication, leading to information disclosure and potential denial of service in libsoup-consuming applications.

Affected Products

GNOME libsoup library (see GNOME libsoup Issue #447)
Red Hat Enterprise Linux distributions shipping libsoup (see Red Hat CVE-2025-4969 Advisory)
Applications and services that link against libsoup for HTTP parsing

Discovery Timeline

2025-05-21 - CVE-2025-4969 published to the National Vulnerability Database
2026-06-30 - Last updated in NVD database

Technical Details for CVE-2025-4969

Vulnerability Analysis

The vulnerability resides in the multipart HTTP message parsing logic of libsoup. When processing multipart request bodies, libsoup fails to correctly validate that the message has been properly terminated by its boundary marker. An attacker who submits a crafted multipart body without a valid closing boundary can cause the parser to continue reading past the end of the allocated buffer.

Out-of-bounds reads in HTTP parsers commonly return adjacent heap contents to the caller or into log output. Depending on how the consuming server handles the parsed data, an attacker may recover fragments of process memory or cause the process to abort. The network-reachable attack surface makes any exposed service that parses multipart uploads a target.

Root Cause

The root cause is missing termination validation in the multipart body parser. The parser advances through the message expecting a boundary delimiter to signal the end of a part, but does not enforce that the boundary is present before the buffer boundary. This produces classic [CWE-125] out-of-bounds read behavior at the parsing layer rather than at a transport layer.

Attack Vector

Exploitation requires only that an attacker reach an HTTP endpoint served or proxied by a libsoup-consuming process. No authentication or user interaction is needed. The attacker submits a Content-Type: multipart/* request whose body omits or corrupts the final boundary marker. Refer to the Red Hat Bug Report #2367552 and GNOME libsoup Issue #447 for the reproducer details.

No verified public exploit code is currently available. The vulnerability is described in prose rather than reproduced here because no verified proof-of-concept has been published.

Detection Methods for CVE-2025-4969

Indicators of Compromise

Repeated multipart HTTP requests with malformed or missing closing boundary markers in web server or reverse proxy logs.
Crashes, segmentation faults, or SIGABRT events in processes linked against libsoup.
Unusual memory contents appearing in HTTP responses, error pages, or application logs following multipart POST requests.

Detection Strategies

Inspect HTTP request bodies at a reverse proxy or web application firewall for multipart/form-data requests that lack a terminating --boundary-- sequence.
Correlate crash telemetry from libsoup-linked services with inbound HTTP request logs to identify pre-crash payloads.
Enumerate installed package versions across Linux fleets and flag hosts running unpatched libsoup builds.

Monitoring Recommendations

Enable core dump collection for services that consume libsoup and forward crash metadata to a central log platform.
Monitor HTTP endpoints for spikes in malformed multipart requests originating from a small number of source addresses.
Track process restart counts on hosts running libsoup-based daemons to detect repeated exploitation attempts.

How to Mitigate CVE-2025-4969

Immediate Actions Required

Apply the libsoup security update provided by your Linux distribution as soon as it is available.
Restart all long-running services that link against libsoup after patching so the updated library is loaded.
Restrict network exposure of internal services that parse multipart HTTP requests using libsoup.

Patch Information

Red Hat tracks the fix and affected packages in the Red Hat CVE-2025-4969 Advisory. Upstream fix coordination is available in GNOME libsoup Issue #447. Administrators should apply distribution-provided libsoup updates and confirm dependent services have been restarted to load the patched library.

Workarounds

Place a hardened reverse proxy in front of libsoup-based services and reject multipart requests without a valid closing boundary.
Disable multipart request handling in exposed applications where the feature is not required.
Limit HTTP request body size on upstream proxies to reduce the attack surface for malformed multipart payloads.

bash

# Verify installed libsoup version and refresh dependent services after patching
rpm -q libsoup libsoup3
dnf update libsoup libsoup3
systemctl list-units --type=service --state=running | \
  xargs -I{} systemctl restart {}