# CVE-2026-95509: Qt QString buffer overflow in String.arg() with Latin-1 encoding

Source: https://junglewise.ai/threats/cve-2026-95509-strings-optimized-for-latin-1-displaying-latin-1-characters-cause  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-29. Updated: 2026-09-29  
License: CC BY 4.0 with a link back

CVE-2026-95509 · Severity: info · Published 2026-09-29

A buffer size calculation error in Qt's QString class causes an out-of-bounds read when formatting strings optimized for Latin-1 character encoding. An application using Qt to process untrusted string data could crash or leak memory contents.

Technologies: [Qt Framework](https://junglewise.ai/threats/technologies/qt-qt-framework). Vendors: [Qt](https://junglewise.ai/threats/vendors/qt).

## Quick answers

**Is CVE-2026-95509 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-95509 being exploited in the wild.

**How severe is CVE-2026-95509?** Informational severity, published 29 September 2026.

**Which products and versions are affected?** Qt Framework <UNKNOWN>.

**Is there a fix for CVE-2026-95509?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-95509 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-95509?** Check whether you run Qt Framework 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

Out-of-bounds read vulnerability in QString.arg() formatting function due to incorrect buffer size calculation for Latin-1 optimized strings. The vulnerability is triggered when formatting Latin-1 characters in strings marked for Latin-1 optimization, allowing an attacker to read past allocated memory bounds via crafted string input.

## Affected products

- Qt Qt Framework <UNKNOWN>

## Timeline

- 2026-09-29: disclosed

## References

- [https://wiki.qt.io/List_of_known_vulnerabilities_in_Qt_products](https://wiki.qt.io/List_of_known_vulnerabilities_in_Qt_products)

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