# CVE-2026-55783: M2Team NanaZip NULL pointer dereference in NanaZip.Codecs archive handlers

Source: https://junglewise.ai/threats/cve-2026-55783-m2team-nanazip-null-pointer-dereference-in-nanazip-codecs-archive  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-10. Updated: 2026-07-10  
License: CC BY 4.0 with a link back

CVE-2026-55783 · Severity: info · CVSS 2.4 · Published 2026-07-10

NanaZip is an open-source file archiver for Windows. A flaw in how the application handles certain archive types (such as WebAssembly or ElectronAsar) can cause the program to crash when a user attempts to test or extract all files from a specially crafted archive. This results in a denial of service where the application becomes unresponsive or closes unexpectedly during file operations.

Technologies: [M2Team NanaZip](https://junglewise.ai/threats/technologies/nanazip). Vendors: [M2Team](https://junglewise.ai/threats/vendors/m2team).

## Quick answers

**Is CVE-2026-55783 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55783 being exploited in the wild.

**How severe is CVE-2026-55783?** Informational severity, with a CVSS score of 2.4, published 10 July 2026.

**Which products and versions are affected?** M2Team NanaZip < 6.5.1749.0.

**Is there a fix for CVE-2026-55783?** A patch was published on 2026-06-16: Fixed in version 6.5.1749.0 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-55783 attacked?** It is attacked with local access, in a network appliance.

**Am I affected by CVE-2026-55783?** Check whether you run M2Team NanaZip 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

A NULL pointer dereference exists in NanaZip's seven in-house IInArchive handlers within NanaZip.Codecs. When the archive engine signals a 'test' or 'extract all' operation, it passes a NULL Indices array and a NumItems value of 0xFFFFFFFF. The vulnerable handlers (WebAssembly, ElectronAsar, Zealfs, Romfs, Ufs, Littlefs, and DotNetSingleFile) fail to check for the NULL array before dereferencing it during the GetStream call. An attacker can trigger this by providing a malicious archive file that causes a process crash when the victim performs standard extraction or testing actions. The issue is resolved in version 6.5.1749.0 by correctly using the pre-computed ActualFileIndex.

## Affected products

- M2Team NanaZip < 6.5.1749.0

## Timeline

- 2026-06-16: patched: Fixed in version 6.5.1749.0
- 2026-06-16: advisory: GitHub Security Advisory GHSA-q67r-9cfh-xc29 published
- 2026-07-10: disclosed: CVE-2026-55783 published to NVD

## References

- [https://github.com/M2Team/NanaZip/commit/5d74d90b737ac7096e5d944a5a3070c5c6a8f894](https://github.com/M2Team/NanaZip/commit/5d74d90b737ac7096e5d944a5a3070c5c6a8f894)
- [https://github.com/M2Team/NanaZip/releases/tag/6.5.1749.0](https://github.com/M2Team/NanaZip/releases/tag/6.5.1749.0)
- [https://github.com/M2Team/NanaZip/security/advisories/GHSA-q67r-9cfh-xc29](https://github.com/M2Team/NanaZip/security/advisories/GHSA-q67r-9cfh-xc29)

## Related threats

- [NanaZip SquashfsHandler heap out-of-bounds read and information disclosure](https://junglewise.ai/threats/cve-2026-54616-nanazip-squashfshandler-heap-out-of-bounds-read-and-information)
- [M2Team NanaZip uncontrolled memory allocation in WebAssembly handler](https://junglewise.ai/threats/cve-2026-55782-m2team-nanazip-uncontrolled-memory-allocation-in-webassembly)
- [M2Team NanaZip memory exhaustion in UFS and FFS image handler](https://junglewise.ai/threats/cve-2026-55781-m2team-nanazip-memory-exhaustion-in-ufs-and-ffs-image-handler)
- [M2Team NanaZip uncaught exception in .NET single-file handler](https://junglewise.ai/threats/cve-2026-55780-m2team-nanazip-uncaught-exception-in-net-single-file-handler)
- [M2Team NanaZip heap out-of-bounds read in AVB vbmeta parser](https://junglewise.ai/threats/cve-2026-47223-m2team-nanazip-heap-out-of-bounds-read-in-avb-vbmeta-parser)