CVE-2026-20915

Insufficiently protected credentials in the host and folder configuration endpoints of the REST API in Checkmk <2.5.0p15, <2.4.0p37, <2.3.0p51 and 2.2.0 (EOL) allows an authenticated user who may view a host's configuration to read stored SNMP community strings, SNMPv3 auth and privacy pass phrases and IPMI passwords in clear text from GET responses, although the setup GUI never displays these values.

Improper neutralization of newlines in filter values in the monitoring host and service list APIs in Checkmk <2.5.0p14 allows an authenticated user to inject additional Livestatus query headers, bypassing object visibility restrictions in count queries to infer information about hosts and services outside their contact groups and occupying web server and Livestatus workers for an attacker-controlled duration.

In Checkmk versions <2.4.0p23, <2.3.0p45, and 2.2.0, there is a vulnerability related to the exposure of the session signing secret. An administrator of a remote site with config sync enabled can hijack sessions on the central site by forging session cookies.

Improper handling of highly compressed data (data amplification) in Checkmk <2.5.0p14, <2.4.0p37, <2.3.0p51 and 2.2.0 (EOL) allows an attacker who controls a host registered for push mode to exhaust the memory of the agent receiver by sending a small zlib compressed payload that decompresses to an arbitrary size.

In Checkmk versions before 2.5.0p10, improper certificate validation allows a relay and a push agent sharing the same UUID to reuse each other's mTLS certificate to authenticate against agent receiver endpoints in either direction, because the endpoints do not verify that the certificate was issued by their own root certificate.

Missing authorization in Checkmk versions <2.5.0p12, <2.4.0p36, <2.3.0p50 and all 2.2.0 versions allows an authenticated user who knows the ID of a background job to view that job's status and results.

Improper authentication in the agent receiver of Checkmk before 2.5.0p10 allows an unauthenticated remote attacker to bypass mutual TLS client certificate verification of relay endpoints by supplying a fixed placeholder identity in the request URL, resulting in limited impact on integrity and availability. Only Cloud, Ultimate, and Ultimate MT editions are affected.

An incorrect authorization vulnerability in frozen BI aggregations in Checkmk (versions <2.5.0p2, <2.4.0p29, <2.3.0p47, and all 2.2.0) allows an authenticated user with restricted host and service visibility to learn the names and existence of hosts and services they are not authorized to see.

Missing authorization in Checkmk before versions 2.5.0p10, 2.4.0p35, 2.3.0p49, and 2.2.0 (EOL) allows an authenticated user lacking the "Edit foreign Reports" permission to modify reports owned by other users.

Improper permission enforcement in Checkmk versions 2.5.0 before 2.5.0p9, 2.4.0 before 2.4.0p34, 2.3.0 before 2.3.0p49, and 2.2.0 (EOL) allows users without permissions to view and modify BI packs and rules.