Libsoup: libsoup: duplicate host header handling causes host-parsing discrepancy (first- vs last-value wins)

Summary

A flaw in libsoup’s HTTP header handling allows multiple Host: headers in a request and returns the last occurrence for server-side processing. Common front proxies often honor the first Host: header, so this mismatch can cause vhost confusion where a proxy routes a request to one backend but the backend interprets it as destined for another host. This discrepancy enables request-smuggling style attacks, cache poisoning, or bypassing host-based access controls when an attacker supplies duplicate Host headers.

Timeline

1. Dec 11, 2025, 12:30 PM UTCCVE published
2. Dec 11, 2025, 2:49 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: partial

3. Jun 29, 2026, 8:30 PM UTCRecord last updated

Affected versions

• libsoup3

  Version range not reported

• libsoup3

  Version range not reported

• libsoup

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• spice-client-win

  Version range not reported

• libsoup

  Version range not reported

• libsoup

  Version range not reported

• libsoup

  Version range not reported

• libsoup

  Version range not reported

• libsoup

  Version range not reported

• libsoup

  Version range not reported

References 21