CVE-2026-74998Network attack vectorHinoki check available

XSS via unvalidated CSS proxy response

Published Aug 17, 2026 · Updated Aug 17, 2026

Cross-site scripting in Roundcube Webmail 1.6.0 through 1.6.17 and 1.7.0 through 1.7.2 allows remote attackers to run script via MIME sniffing. In program/actions/utils/modcss.php, the CSS proxy accepted proxied responses tagged as text/css or text/plain and re-served them as text/css without validating that the body was actually CSS. Exposure depends on the proxy fetching attacker-controlled or otherwise untrusted content; the vendor fix adds response-body checks that reject obvious HTML or JSON and require basic CSS syntax markers.

CVSS severity7.2
High
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Cross-site scripting in Roundcube Webmail 1.6.0 through 1.6.17 and 1.7.0 through 1.7.2 allows remote attackers to run script via MIME sniffing. In program/actions/utils/modcss.php, the CSS proxy accepted proxied responses tagged as text/css or text/plain and re-served them as text/css without validating that the body was actually CSS. Exposure depends on the proxy fetching attacker-controlled or otherwise untrusted content; the vendor fix adds response-body checks that reject obvious HTML or JSON and require basic CSS syntax markers.

The record

CVE
CVE-2026-74998
Published
Aug 17, 2026
Updated
Aug 17, 2026
Vendor
Roundcube
Product
Roundcube Webmail
Classifications
CWE-79, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 17, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 17, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.6.0 <1.6.18
  2. Affected versionversion=1.7.0 <1.7.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Roundcube · Roundcube Webmailversion=1.6.0 <1.6.18; version=1.7.0 <1.7.3

Published CVSS scores

7.2GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo