VulnerabilityPublished 2 Dec 2025

CVE-2025-41066: Horde Groupware · Information Exposure

Affects Horde GroupwareSource CVE Database V5

Not known to be exploited · CVSS 6.9 Medium.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 4.0 base score

6.9Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 15% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: Low
Vulnerable system integrity: None
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Horde Groupware	Affected =5.2.22	Fixed in–

AI-suggested

Apply official patches or updates from the Horde project as soon as they become available to remediate the vulnerability.
In the absence of patches, implement web application firewall (WAF) rules to detect and block requests to /imp/attachment.php containing the 'id' and 'u' parameters from untrusted sources.
Restrict access to the Horde Groupware interface and related endpoints to trusted IP ranges or via VPN to reduce exposure.
Enable detailed logging and monitoring of HTTP requests to detect patterns indicative of user enumeration attempts, such as repeated requests with varying 'u' parameter values.
Implement rate limiting on the vulnerable endpoint to hinder automated enumeration attempts.
Educate users and administrators about the risks of user enumeration and encourage strong password policies and multi-factor authentication to mitigate risks from subsequent attacks.
Conduct regular security assessments and penetration testing focusing on user enumeration and related vulnerabilities in collaboration tools.

Description

CVE-2025-41066 is a user enumeration vulnerability in Horde Groupware version 5.2.22 that allows unauthenticated attackers to verify valid user accounts by sending crafted HTTP requests to the /imp/attachment.php endpoint. The server’s response behavior differs based on user existence, leaking sensitive information about valid usernames. This vulnerability has a CVSS score of 6.9 (medium severity) and requires no authentication or user interaction to exploit. While it does not directly allow access to data or system compromise, it facilitates reconnaissance that can be leveraged in further attacks such as phishing or brute force. No known exploits are currently reported in the wild. European organizations using Horde Groupware 5.

Impact

For European organizations, the primary impact of CVE-2025-41066 lies in the facilitation of reconnaissance activities by attackers. By enumerating valid user accounts, adversaries can tailor phishing campaigns, credential stuffing, or brute force attacks more effectively, increasing the risk of account compromise. This is particularly concerning for organizations handling sensitive or regulated data, such as government agencies, financial institutions, and healthcare providers, where user account compromise can lead to data breaches or unauthorized access to critical systems. Additionally, the exposure of valid usernames can damage organizational reputation and trust. Since Horde Groupware is used for collaboration and communication, compromised accounts could lead to further lateral movement within networks. The vulnerability’s ease of exploitation and unauthenticated access make it a low barrier threat that can be exploited remotely. European entities relying on Horde Groupware 5.2.22 should consider this vulnerability a significant risk vector in their threat landscape.

CWE-200Exposure of Sensitive Information to an Unauthorized Actor (opens in a new tab)
Class weaknessLikelihood of exploit: HighCWE Top 25 (2025): #20OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information.
MITRE discourages mapping vulnerabilities to this broad entry; the root cause is usually a more specific weakness.
Architecture and Design · Separation of Privilege
Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.
OWASP Cheat Sheets
Error Handling (opens in a new tab)
Logging (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V8.3.4 (opens in a new tab)
V14.3.3 (opens in a new tab)
V7.3.3 (opens in a new tab)
Attack patterns
Subverting Environment Variable Values (opens in a new tab)
ICMP Echo Request Ping (opens in a new tab)
TCP SYN Scan (opens in a new tab)
Enumerate Mail Exchange (MX) Records (opens in a new tab)
DNS Zone Transfers (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

incibe.es/en/incibe-cert/notices/aviso/disclosure-sensitive-information-horde-groupware (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 9 Dec 2025, 14:38 UTC

WeaknessesCWE-200

Technical details

References

Community reviews

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