CVE-2025-41066: Horde Groupware v5.2.22 has a user enumeration vulnerability that allows an unauthenticated attacker to determ

Routine

MEDIUM 5.3REMOTEDOWNGRADE

CVE-2025-41066 is a medium-severity flaw (CVSS 5.3) affecting groupware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Horde Groupware v5.2.22 has a user enumeration vulnerability that allows an unauthenticated attacker to determine the existence of valid accounts on the system. To exploit the vulnerability, an HTTP request must be sent to ‘/imp/attachment.php’ including the parameters ‘id’ and ‘u’. If the specified user exists, the server will return the download of an empty file; if it does not exist, no download will be initiated, which unequivocally reveals t

Why this priority

Remotely exploitable, no login, no user action

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

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 84%)
CISA exploited list	No
Weakness	CWE-200
Published	2025-12-02
Last modified	2026-10-18

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

Last updated 2026-10-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-12-02 14:16 UTCPublished CVE record published
2026-10-18 18:10 UTCUpdated Record last modified

horde groupware DOWNGRADE

Affected: 5.2.22

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.2.22

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 5.2.22 (Debian / Ubuntu)

apt-cache madison groupware sudo apt install groupware=<VERSION_BEFORE_5.2.22> sudo apt-mark hold groupware

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

dnf --showduplicates list groupware sudo dnf downgrade groupware-<VERSION_BEFORE_5.2.22> sudo dnf versionlock add groupware

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-2025-41066?

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

Is CVE-2025-41066 being exploited?

CVE-2025-41066 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-2025-41066 affect?

CVE-2025-41066 affects groupware. Severity is medium (CVSS 5.3). Horde Groupware v5.2.22 has a user enumeration vulnerability that allows an unauthenticated attacker to determine the existence of valid accounts on the system. To exploit the vulnerability, an HTTP request must be sent to ‘/imp/attachment.

How urgent is CVE-2025-41066?

Priority 27/100. Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

References

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