CVE-2026-55780 M2Team CVE debrief

Who should care

Users of NanaZip versions prior to 6.5.1749.0 should update to the latest version to prevent potential crashes caused by crafted bundles. This vulnerability has a low CVSS score and is considered LOW severity, but operators and security teams should still review the affected scope and vendor guidance. Security teams should verify NanaZip installations to ensure they are up-to-date and monitor NanaZip logs for potential exploitation attempts.

Technical summary

CVE-2026-55780 is a vulnerability in NanaZip's .NET single-file bundle handler. The handler sizes its extraction buffer based on the bundle entry Size field, which is only checked for sign and not validated against the real file size. A crafted bundle can cause an attacker-chosen allocation inside Extract, leading to a std::bad_alloc or std::length_error that can escape across the COM STDMETHODCALLTYPE boundary and crash the process. This issue has a CVSS score of 2.4 and is considered LOW severity. The vulnerability was fixed in version 6.5.1749.0.

Defensive priority

Low priority, as the vulnerability requires a crafted bundle and has a low CVSS score. However, security teams should still review the affected scope and vendor guidance, and verify NanaZip installations to ensure they are up-to-date.

Recommended defensive actions

• Update NanaZip to version 6.5.1749.0 or later
• Verify NanaZip installations to ensure they are up-to-date
• Monitor NanaZip logs for potential exploitation attempts
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-10T17:16:59.733Z and has not been modified since then. The NVD entry is currently Deferred. There is limited information available about the vulnerability, and defenders should verify the affected scope and severity with the vendor. The NanaZip .NET single-file bundle handler vulnerability allows an attacker to cause a process crash by crafting a bundle that triggers a std::bad_alloc or std::length_error. This issue was fixed in version 6.5.1749.0. Evidence limits suggest that further details may be required to fully understand the vulnerability.

Official resources