CVE-2025-4476
📋 TL;DR
A denial-of-service vulnerability in libsoup HTTP client library allows attackers to crash client applications by sending crafted 401 responses with malformed WWW-Authenticate headers. This affects any application using vulnerable libsoup versions to connect to external HTTP servers. Attackers must trick clients into connecting to malicious servers they control.
💻 Affected Systems
- libsoup HTTP client library
- applications using libsoup (GNOME applications, various Linux utilities)
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Client application crashes repeatedly when connecting to attacker-controlled servers, causing persistent denial-of-service for affected users.
Likely Case
Temporary application crashes affecting individual users who encounter malicious servers, requiring application restart.
If Mitigated
Limited impact with proper network controls and updated libraries, potentially causing isolated crashes but no persistent disruption.
🎯 Exploit Status
Exploitation requires attacker to control HTTP server that client connects to; no authentication needed on client side.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor-specific updates (Red Hat, Ubuntu, etc.)
Vendor Advisory: https://access.redhat.com/security/cve/CVE-2025-4476
Restart Required: Yes
Instructions:
1. Check your distribution's security advisories. 2. Update libsoup package via package manager. 3. Restart affected applications. 4. Verify version is patched.
🔧 Temporary Workarounds
Network filtering
allBlock or monitor connections to untrusted HTTP servers
Application configuration
allConfigure applications to avoid connecting to unknown HTTP servers
🧯 If You Can't Patch
- Implement network segmentation to restrict HTTP connections to trusted servers only
- Monitor for application crashes and investigate connections preceding crashes
🔍 How to Verify
Check if Vulnerable:
Check libsoup version against vendor security advisories; examine if applications use libsoup for HTTP client operationsCheck Version:
ldconfig -p | grep libsoup or check package manager (rpm -q libsoup, dpkg -l libsoup*)Verify Fix Applied:
Verify libsoup package version matches patched version from vendor advisory📡 Detection & Monitoring
Log Indicators:
- Application crash logs mentioning libsoup
- Unexpected application termination after HTTP requests
Network Indicators:
- HTTP 401 responses with WWW-Authenticate headers from unknown servers
- Connections to suspicious IP addresses
SIEM Query:
Application:crash AND Process:libsoup OR Network:http_response_code:401