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CVE-2026-3089: CVE-2026-3089: Authenticated Path Traversal in Actual Sync Server

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CVE-2026-3089: Authenticated Path Traversal in Actual Sync Server

Vulnerability ID: CVE-2026-3089
CVSS Score: 5.3
Published: 2026-03-10

CVE-2026-3089 is an authenticated path traversal vulnerability in Actual Sync Server prior to version 26.3.0. By manipulating the x-actual-file-id HTTP header, an authenticated attacker can bypass directory restrictions to read or write arbitrary files on the host filesystem. This flaw stems from a lack of input validation when constructing file paths for user uploads and downloads.

TL;DR

Actual Sync Server < 26.3.0 is vulnerable to an authenticated path traversal (CWE-22) via the x-actual-file-id header, allowing arbitrary file read/write and potential code execution. Update to version 26.3.0.

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-22
  • Attack Vector: Network
  • CVSS Score: 5.3 (v4.0)
  • Impact: Arbitrary File Read/Write, Potential RCE
  • Exploit Status: Proof-of-Concept Available
  • Authentication: Required (Valid Token)
  • Patched Version: 26.3.0

Affected Systems

  • Actual Sync Server prior to 26.3.0
  • Actual Sync Server: < 26.3.0 (Fixed in: 26.3.0)

Code Analysis

Commit: 18072e1

Fix path traversal vulnerability by enforcing strict fileId validation

Exploit Details

  • Fluid Attacks: Proof of Concept utilizing curl to write arbitrary files

Mitigation Strategies

  • Upgrade Actual Sync Server to version 26.3.0 or later
  • Deploy Web Application Firewall (WAF) rules to inspect and block path traversal sequences in the x-actual-file-id header
  • Run the server process within a restricted container environment with read-only volume mounts where appropriate
  • Enforce least privilege for the service account executing the Actual Sync Server

Remediation Steps:

  1. Identify all deployments of Actual Sync Server prior to version 26.3.0
  2. Stop the running service to prevent potential exploitation during the upgrade
  3. Update the application binaries or container image to version 26.3.0
  4. Restart the service and verify normal operations
  5. Audit access logs for anomalous file requests containing ../ sequences in the affected endpoints

References

Read the full report for CVE-2026-3089 on our website for more details including interactive diagrams and full exploit analysis.

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