CVE-2026-77021 Missing decompression size limit in agent receiver allows memory exhaustion via push agent data
An attacker controlling a push-mode host can exhaust agent receiver memory by sending highly compressed data, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-77021?
CVE-2026-77021 is a medium-severity denial of service vulnerability in Checkmk, published on 21 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
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.
Weakness: CWE-409
Which versions are affected by CVE-2026-77021?
How do I fix CVE-2026-77021?
No fix has been published for CVE-2026-77021 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-77021 being exploited?
There is no known exploitation of CVE-2026-77021 in the wild and no public exploit code.
Sources
Also known as GHSA-5q8h-fhcg-2395.