# CVE-2026-39894: Cacti data corruption via locale-dependent decimal formatting in rrdtool_function_update

Source: https://junglewise.ai/threats/cve-2026-39894-cacti-data-corruption-via-locale-dependent-decimal-formatting-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-24. Updated: 2026-06-24  
License: CC BY 4.0 with a link back

CVE-2026-39894 · Severity: low · CVSS 2.9 · Published 2026-06-24

Cacti is an open-source platform used for monitoring network performance and managing system faults. A technical issue in how the software handles numbers on servers configured with certain international regional settings (locales) can cause monitoring data to become corrupted or misaligned. While this does not allow an outside attacker to steal data, it can lead to inaccurate reporting and loss of historical performance metrics, potentially impacting operational decision-making.

Technologies: [Cacti](https://junglewise.ai/threats/technologies/cacti). Vendors: [Cacti](https://junglewise.ai/threats/vendors/cacti).

## Quick answers

**Is CVE-2026-39894 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-39894 being exploited in the wild.

**How severe is CVE-2026-39894?** Low severity, with a CVSS score of 2.9, published 24 June 2026.

**Which products and versions are affected?** Cacti <= 1.2.30.

**Is there a fix for CVE-2026-39894?** A patch was published on 2026-06-24: CVE published and fix confirmed in version 1.2.31 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-39894 attacked?** It is attacked with local access, in a network appliance.

**Am I affected by CVE-2026-39894?** Check whether you run Cacti at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the `rrdtool_function_update()` function within `lib/rrd.php`. The application uses PHP string interpolation to construct RRDtool update commands. Because PHP's float-to-string conversion is locale-sensitive, servers configured with an `LC_NUMERIC` locale that uses commas as decimal separators (e.g., German or French) will produce strings like '1,5' instead of '1.5'. Since RRDtool strictly expects a period as the decimal separator, this causes the command parser to shift metric data into incorrect columns or drop the data entirely. This is a data integrity issue that requires a specific server locale configuration to manifest. The issue is addressed in version 1.2.31 by enforcing strict dot-decimal formatting at the IPC boundary.

## Affected products

- Cacti Cacti <= 1.2.30

## Timeline

- 2026-04-06: disclosed: Issue reported via GitHub
- 2026-06-18: advisory: Project security advisory published
- 2026-06-24: patched: CVE published and fix confirmed in version 1.2.31

## References

- [https://github.com/Cacti/cacti/commit/d2a698854956e9e4e53da9eab5b5719ae40e6893](https://github.com/Cacti/cacti/commit/d2a698854956e9e4e53da9eab5b5719ae40e6893)
- [https://github.com/Cacti/cacti/issues/7011](https://github.com/Cacti/cacti/issues/7011)
- [https://github.com/Cacti/cacti/security/advisories/GHSA-23g4-vf2j-94w4](https://github.com/Cacti/cacti/security/advisories/GHSA-23g4-vf2j-94w4)

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