CVE-2025-40631: HTTP host header injection vulnerability in Icewarp Mail Server affecting version 11.4.0

Routine

MEDIUM 6.1DOWNGRADE

CVE-2025-40631 is a medium-severity flaw (CVSS 6.1) affecting mail server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

HTTP host header injection vulnerability in Icewarp Mail Server affecting version 11.4.0. By modifying the Host header and adding a payload, arbitrary JavaScript code can be executed on page load. The user must interact with a malicious link to be redirected.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.2% (top 87%)
CISA exploited list	No
Weakness	CWE-644
Published	2025-05-16
Last modified	2026-06-17

Publisher (CNA): Spanish National Cybersecurity Institute, S.A. (INCIBE) · Vendor: icewarp

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-05-16 11:15 UTCPublished CVE record published
2026-06-17 09:21 UTCUpdated Record last modified

icewarp mail server DOWNGRADE

Affected: 11.4.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 11.4.0

1. Check installed version

apt-cache policy mail-server || rpm -q mail-server || mail-server --version

2. No fixed release: DOWNGRADE to a release before 11.4.0 (Debian / Ubuntu)

apt-cache madison mail-server sudo apt install mail-server=<VERSION_BEFORE_11.4.0> sudo apt-mark hold mail-server

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list mail-server sudo dnf downgrade mail-server-<VERSION_BEFORE_11.4.0> sudo dnf versionlock add mail-server

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-2025-40631?

mail server: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-40631 being exploited?

CVE-2025-40631 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-2025-40631 affect?

CVE-2025-40631 affects mail server. Severity is medium (CVSS 6.1). HTTP host header injection vulnerability in Icewarp Mail Server affecting version 11.4.0. By modifying the Host header and adding a payload, arbitrary JavaScript code can be executed on page load. The user must interact with a malicious lin

How urgent is CVE-2025-40631?

Priority 25/100. No elevated risk signals yet.

Related CVEs

CVE-2025-2848 MEDIUM 6.3 UPGRADE A vulnerability in Synology Mail Server allows remote authenticated attackers to read and write non-sensitive
CVE-2021-36580 MEDIUM 6.1 UPGRADE UPGRADE Open Redirect vulnerability exists in IceWarp MailServer IceWarp Server Deep Castle 2 Update 1 (13.0.1.2) via
CVE-2025-40632 MEDIUM 6.1 DOWNGRADE Cross-site scripting (XSS) in Icewarp Mail Server affecting version 11.4.0
CVE-2025-40630 MEDIUM 6.1 DOWNGRADE Open redirection vulnerability in IceWarp Mail Server affecting version 11.4.0
CVE-2023-39700 MEDIUM 6.1 DOWNGRADE IceWarp Mail Server v10.4.5 was discovered to contain a reflected cross-site scripting (XSS) vulnerability via

References

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