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CVE-2026-77021

Missing decompression size limit in agent receiver allows memory exhaustion via push agent data

MEDIUM
5.3
CVSS Score
Published: September 21, 2026 at 10:57 AM UTC
Updated: September 21, 2026 at 08:17 PM UTC
1 product affected across 1 vendorCheckmk

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.4%
SSVC
No known exploit

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Checkmk· Checkmk
95%
2.3.0 ≤ v < 2.3.0p512.4.0 ≤ v < 2.4.0p372.5.0 ≤ v < 2.5.0p142.2.02.3.02.4.02.5.0
Affected range stops below 2.3.0p51, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.4.0p37, so it looks safe — our inference, not a vendor statement
Affected range stops below 2.5.0p14, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (1)

Vendor Advisory
Source: cverecord
https://checkmk.com/werk/22116

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUMCheckmk
Vector?

Quick Info

StatusDEFERRED
CWE
CWE-409

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