CVE-2026-27557 Overview
CVE-2026-27557 is a path traversal vulnerability [CWE-35] in the /index.php/view_uploaded_iodd_file endpoint. An unauthenticated remote attacker can abuse the endpoint to read arbitrary files, including the SSH server's private keys. Successful exploitation exposes cryptographic material used to authenticate the SSH service. Attackers can leverage the stolen keys to impersonate the device, decrypt intercepted sessions, or pivot into connected systems. The issue is tracked in multiple CERT@VDE advisories and requires no user interaction or prior privileges.
Critical Impact
Unauthenticated remote attackers can read SSH private keys, enabling identity impersonation and downstream compromise of trust relationships that depend on the affected device.
Affected Products
- Products covered under CERT@VDE advisory VDE-2026-014
- Products covered under CERT@VDE advisory VDE-2026-027
- Products covered under CERT@VDE advisory VDE-2026-028
Discovery Timeline
- 2026-09-16 - CVE-2026-27557 published to the National Vulnerability Database (NVD)
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-27557
Vulnerability Analysis
The flaw resides in the /index.php/view_uploaded_iodd_file PHP endpoint. The endpoint accepts a file name or path parameter and returns the contents of the referenced file. Insufficient validation of the supplied path allows an attacker to escape the intended upload directory using traversal sequences such as ../. Because the endpoint does not enforce authentication, any network-reachable client can issue the request. Successful requests return the raw contents of arbitrary files readable by the web server process, including the SSH server's private key material.
Root Cause
The root cause is improper limitation of a pathname to a restricted directory, classified as [CWE-35] Path Traversal ('.../...//'). The endpoint concatenates user-supplied input into a file path without canonicalizing the result or verifying that it stays within an allow-listed directory. No authentication check gates the endpoint, which compounds the exposure.
Attack Vector
Exploitation occurs over the network against the HTTP interface of the affected device. The attacker sends a crafted HTTP GET or POST request to /index.php/view_uploaded_iodd_file with a path parameter containing directory traversal sequences pointing at the SSH server's private key file. No credentials, tokens, or user interaction are required. Consult the CERT@VDE advisories listed in the references for the exact request format and affected parameter names.
Detection Methods for CVE-2026-27557
Indicators of Compromise
- HTTP requests to /index.php/view_uploaded_iodd_file containing traversal patterns such as ../, ..%2f, or encoded variants in query parameters.
- Web server access log entries showing anonymous reads of the endpoint returning non-standard file sizes consistent with key material.
- Unexpected SSH logins to other systems using the affected device's host key or associated identities.
Detection Strategies
- Deploy web application firewall rules that block path traversal sequences targeting the view_uploaded_iodd_file endpoint.
- Correlate HTTP access logs with SSH authentication logs to identify reuse of exfiltrated keys across the environment.
- Alert on any HTTP response from the endpoint whose body matches SSH private key headers such as -----BEGIN OPENSSH PRIVATE KEY----- or -----BEGIN RSA PRIVATE KEY-----.
Monitoring Recommendations
- Monitor perimeter and internal network traffic to management interfaces of affected devices for anomalous requests to the vulnerable endpoint.
- Track SSH host key fingerprints and alert on unexpected reuse of a device's host key from a different source address.
- Review CERT@VDE advisories VDE-2026-014, VDE-2026-027, and VDE-2026-028 for vendor-published detection artifacts.
How to Mitigate CVE-2026-27557
Immediate Actions Required
- Restrict network access to the device's HTTP management interface using firewall rules or VLAN segmentation until a patch is applied.
- Rotate the SSH server host keys and any user or automation keys stored on the device after applying the fix.
- Audit connected systems for SSH authorized_keys or known_hosts entries that reference the affected device and revoke trust where appropriate.
Patch Information
Refer to the vendor advisories published by CERT@VDE for patch availability and fixed versions: CERT VDE Advisory VDE-2026-014, CERT VDE Advisory VDE-2026-027, and CERT VDE Advisory VDE-2026-028. Apply the vendor-supplied firmware or software update as soon as it becomes available.
Workarounds
- Block external access to /index.php/view_uploaded_iodd_file at an upstream reverse proxy or WAF until firmware is updated.
- Disable the affected web feature if the device configuration permits it and the functionality is not required.
- Enforce network-layer access controls that limit management-plane access to trusted administrative hosts only.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
