Vulnerability · Published Sep 21, 2026 · Assigned by Checkmk
CVE-2026-77021Missing decompression size limit in agent receiver allows memory exhaustion via push agent data
Medium 5.3
In plain English
A medium-severity security flaw in Checkmk from Checkmk GmbH. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 32% of all known vulnerabilities).
Severity (CVSS 4.0)5.3Medium
Exploit odds (30 days)0.4%top 67.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Checkmk GmbH | Checkmk | 2.5.0 – before 2.5.0p142.4.0 – before 2.4.0p372.3.0 – before 2.3.0p512.2.0 |
Weakness: CWE-409 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
References
- https://checkmk.com/werk/22116 vendor-advisory