CVE-2026-74998: In Roundcube Webmail before 1.6.18 and 1.7.x before 1.7.3, responses from the CSS (Cascading Style Sheets) pro

This month

HIGH 7.2REMOTEUPGRADE

CVE-2026-74998 is a high-severity flaw (CVSS 7.2) affecting webmail. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In Roundcube Webmail before 1.6.18 and 1.7.x before 1.7.3, responses from the CSS (Cascading Style Sheets) proxy were not validated, which may result in information disclosure or XSS (cross-site scripting) via MIME sniffing.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.2 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-79
Published	2026-08-17
Last modified	2026-09-08

Publisher (CNA): MITRE · Vendor: roundcube

Last updated 2026-09-08 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-17 13:16 UTCPublished CVE record published
2026-09-08 19:10 UTCUpdated Record last modified

roundcube webmail UPGRADE

Affected: >= 1.6.0 and < 1.6.18 · >= 1.7.0 and < 1.7.3

Fixed in: 1.6.18, 1.7.3

Safe to downgrade to: a release before 1.6.0

1. Check installed version

apt-cache policy webmail || rpm -q webmail || webmail --version

2. UPGRADE to 1.6.18 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade webmail

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade webmail

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.6.0 (Debian / Ubuntu)

apt-cache madison webmail sudo apt install webmail=<VERSION_BEFORE_1.6.0> sudo apt-mark hold webmail

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list webmail sudo dnf downgrade webmail-<VERSION_BEFORE_1.6.0> sudo dnf versionlock add webmail

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-74998?

webmail: upgrade to 1.6.18, 1.7.3. Exact commands for each OS are on this page.

Is CVE-2026-74998 being exploited?

CVE-2026-74998 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-74998 affect?

CVE-2026-74998 affects webmail. Severity is high (CVSS 7.2). In Roundcube Webmail before 1.6.18 and 1.7.x before 1.7.3, responses from the CSS (Cascading Style Sheets) proxy were not validated, which may result in information disclosure or XSS (cross-site scripting) via MIME sniffing.

How urgent is CVE-2026-74998?

Priority 40/100. High severity; Remotely exploitable, no login, no user action

Software pages

Roundcube vulnerabilities

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References

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