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TI-2026-40312 Aliases CVE-2026-55850

Element Web: A malicious homeserver can inject HTML in Element Web using its homepage

Priority LOW 25CWE-79Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Passive
Attack complexity
Low
Attack requirements
None
Impact type
Cross-site scripting
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-79.

Summary

Element Web is a Matrix web client built using the Matrix React SDK. Prior to 1.12.22, EmbeddedPage in apps/web/src/components/structures/EmbeddedPage.tsx renders homeserver-supplied homepage content through dangerouslySetInnerHTML without passing it through sanitizedHtmlNode. A malicious homeserver can provide crafted HTML that Element Web renders on the homepage; the content security policy prevents JavaScript but not phishing HTML. This issue is fixed in version 1.12.22.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00547 46th percentileScored 2026-11-07
Fix Fixed element-web (element-hq): 1.12.22

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
element-hqelement-webbefore 1.12.221.12.22Patch availableCNA
  • element-web Vendorelement-hq Affected before 1.12.22 Fixed in 1.12.22 Patch available CNA

Remediation

  • Fix · CNA element-web (element-hq) Fixed in 1.12.22

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-55850

References

Other 4

  • TI-2024-35327 Synapse allows a a malformed invite to break the invitee's `/sync` CVSS 4.0HIGH 8.7
  • TI-2024-36056 Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders CVSS 4.0HIGH 8.2
  • TI-2024-35318 Synapse allows unsupported content types to lead to memory exhaustion CVSS 4.0HIGH 8.2
  • TI-2022-07650 Remote program execution with user interaction CVSS 3.1HIGH 8.8
  • TI-2026-19372 ESS Community Helm Chart has a weak server key generation method CVSS 4.0CRITICAL 9.2
  • TI-2024-24814 Synapse denial of service through media disk space consumption CVSS 3.1HIGH 7.5
See all 31 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences