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Certificate renewal might incorrectly renew an invalid certificate

Critical
yhabteab published GHSA-7vcf-f5v9-3wr6 May 27, 2025

Package

Icinga 2

Affected versions

≤ 2.14.5

Patched versions

2.14.6, 2.13.12, 2.12.12

Description

Impact

Note

If Icinga 2 is built with OpenSSL 1.1.0 (released in 2016) or later, it is NOT affected by this issue.
This can be checked by running icinga2 --version | grep OpenSSL.

The VerifyCertificate() function can be tricked into incorrectly treating certificates as valid. This allows an attacker to send a malicious certificate request that is then treated as a renewal of an already existing certificate, resulting in the attacker obtaining a valid certificate that can be used to impersonate trusted nodes.

For this to be exploited, a direct TLS connection to a master capable of signing certificates is required. The bug can also be triggered on other nodes. On these, it only results in an incorrect "Received certificate request for CN '[...]' signed by our CA." log message before forwarding the request. That forwarded request is then handled correctly by the master and doesn't trigger the issue.

This only happens with OpenSSL older than version 1.1.0 as it stored a valid flag in the certificate that causes some steps of the verification operation to be skipped. In case this flag is set from a previous operation, this can lead to an incorrect result. The flag in question was removed in OpenSSL 1.1.0, so if Icinga 2 is built with that or a later version, the certificate is always verified completely and the problem doesn't occur.

Note that for example RHEL 7 and derivatives like Amazon Linux 2 ship OpenSSL 1.0.2, hence Icinga 2 is vulnerable on these platforms.

Patches

The problem has been fixed in the following versions:

Users are advised to upgrade Icinga 2 to a fixed version on masters running with OpenSSL 1.0.2 or older immediately.

The source code for the new versions can be found in our Git repository. Updated binary packages are available on packages.icinga.com.

Workarounds

For this to be exploited, a direct TLS connection to a master capable of signing certificates is required, giving two options for a workaround:

  1. Restrict network access to the masters to only trusted entities.
  2. Stop the master from signing any new certificates. This can be achieved by renaming the /var/lib/icinga2/ca directory. Note that this will prevent you from setting up new nodes as well as prevent existing nodes from renewing their certificates. Certificates are renewed around 30 days before their expiry date, so that's only a short-term solution as certificates will eventually expire otherwise.

References

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality Low
Integrity Low
Availability Low

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L

CVE ID

CVE-2025-48057

Weaknesses