Checkmk: Improper Neutralization of Delimiters
CVE-2026-33456 is a high-severity improper neutralization of delimiters vulnerability in Checkmk, with a CVSS 3.1 base score of 7.6 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. The record lists versions 2.5.0b4, 2.4.0p26 as the first without the flaw, so updating Checkmk to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.2% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Checkmk to 2.5.0b4 or 2.4.0p26, whichever matches your release line, or a later version.
- Read the advisory on checkmk.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Checkmk | Checkmk | 2.5.0 up to, but not including, 2.5.0b4; 2.4.0 up to, but not including, 2.4.0p26 | 2.5.0b4, 2.4.0p26 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- LowSome restricted data can be read.
- Integrity
- LowLimited modification of data is possible.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 5.1 | Medium | CNA (checkmk.com) |
| CVSS 3.1 | 7.6 | High | NVD |
Official description
Livestatus injection in the notification test mode in Checkmk <2.5.0b4 and <2.4.0p26 allows an authenticated user with access to the notification test page to inject arbitrary Livestatus commands via a crafted service description.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Neutralization of Delimiters
The product does not neutralize or incorrectly neutralizes delimiters.
How developers prevent this class of flaw
- Developers should anticipate that delimiters will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
- While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
- Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
More Improper Neutralization of Delimiters vulnerabilities (CWE-140)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in Checkmk
- 9.4 Critical severity
- 9.4 Critical severity
- 9.4 Critical severity
- 7.1 High severity
- 8.6 High severity
- 7.8 High severity
Recent Improper Neutralization of Delimiters vulnerabilities
- 8.8 High severity
- 8.8 High severity
- 7.5 High severity
- 7.0 High severity
- 8.8 High severity
- 8.8 High severity
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