CVE-2021-27276

What it actually does

CVE-2021-27276 is a path traversal vulnerability in NETGEAR ProSAFE Network Management System 1.6.0.26 affecting the MibController file-handling logic. The application uses the user-controlled realName parameter in file operations without properly normalizing and constraining the path to an intended directory. A remote attacker can supply traversal sequences to target files outside the expected location and delete arbitrary files. Although the CVSS vector lists low privileges, the vendor description notes that the product’s authentication mechanism can be bypassed, making the practical exposure closer to unauthenticated remote abuse in vulnerable deployments. The main technical consequence is high availability impact and limited integrity impact through arbitrary file deletion.

Why it matters to the business

Successful exploitation can disrupt network management operations by deleting application, configuration, database, log, or operating-system files accessible to the NETGEAR ProSAFE NMS process. This may cause service outages, loss of monitoring visibility, configuration loss, failed backups, or degraded ability to manage network devices. The high EPSS score indicates a meaningful likelihood of exploitation in the wild even though the issue is not currently listed in CISA KEV. Because the product is a network management platform, compromise or disruption can affect operational visibility across many managed devices rather than just a single server.

How an attack unfolds

An attacker first identifies a reachable NETGEAR ProSAFE Network Management System instance running the vulnerable 1.6.0.26 release. The attacker then interacts with the application workflow handled by MibController and abuses weaknesses in the authentication flow to reach functionality that should require a valid session. Once the vulnerable function is reachable, the attacker submits a crafted realName parameter containing directory traversal sequences such as ../ or URL-encoded equivalents. The server fails to validate the resolved file path and performs a delete operation against the attacker-selected path. By choosing sensitive application or system files, the attacker can render the NMS application unstable, erase operational data, remove logs, or trigger a denial-of-service condition.

How to fix it

Upgrade NETGEAR ProSAFE Network Management System to a vendor-fixed release if available from NETGEAR support channels; no fixed version was provided in the supplied advisory data. If the product is no longer supported or a fixed build is unavailable, remove it from service or replace it with a supported network management platform. As interim mitigation, restrict access to the NMS web interface to trusted administrative networks only, place it behind VPN or bastion access, block direct internet exposure, and enforce network-layer allowlisting. Run the service with the least-privileged operating-system account so arbitrary deletion cannot affect files outside the application’s required directories. Maintain offline backups of NMS configuration and data. Monitor and block HTTP requests containing traversal patterns in parameters such as realName, including encoded traversal sequences.

How to confirm the fix worked

Confirm exposure by inventorying all NETGEAR ProSAFE Network Management System installations and verifying whether version 1.6.0.26 is present. Validate remediation by confirming the installed version is newer than the vulnerable release or that the product has been decommissioned. Test that the NMS web interface is not reachable from untrusted networks. Review web application firewall, reverse proxy, and application logs to confirm requests containing traversal sequences in the realName parameter are blocked or rejected. If performing authorized security testing, send a benign traversal probe that targets a non-sensitive canary file in a controlled lab or maintenance window and confirm the application refuses the request and does not delete files outside the intended directory.

Typical attack path

1. Scan for externally reachable or internally reachable NETGEAR ProSAFE Network Management System web interfaces.
2. Fingerprint the version or behavior to determine whether the instance is consistent with vulnerable release 1.6.0.26.
3. Bypass or abuse the weak authentication mechanism to access MibController functionality.
4. Send a crafted request containing a malicious realName parameter with path traversal sequences.
5. Cause the application to delete a file outside the intended directory.
6. Repeat deletion attempts against files needed for application operation, logging, configuration, or data storage to cause service disruption.

How to detect it

To determine whether exploitation already occurred, review HTTP access logs, reverse proxy logs, WAF logs, and NETGEAR ProSAFE NMS application logs for requests to controller functionality involving the realName parameter with directory traversal patterns. Search for both raw and encoded traversal sequences, including ../, ..\, %2e%2e%2f, %2e%2e%5c, double-encoded variants, and attempts to reference sensitive paths. Correlate suspicious requests with application errors, service crashes, restarts, missing files, backup failures, or unexpected changes in file-system metadata. On the host, examine operating-system event logs, file integrity monitoring alerts, endpoint telemetry, and backup logs for deletions by the NMS service account or web application process. Pay particular attention to missing configuration, database, log, or application files around the time of suspicious web requests. Because exploitation may be used to remove evidence, absence of application logs after a suspicious request should itself be treated as a possible indicator.

• realName=../
• realName=..%2f
• realName=%2e%2e%2f
• realName=..%5c
• realName=%2e%2e%5c
• realName=%252e%252e%252f
• realName=%252e%252e%255c
• realName=../../
• realName=..\..\
• MibController
• /etc/passwd
• /etc/shadow
• C:\Windows\System32
• C:\Program Files
• ../WEB-INF
• ..\WEB-INF

What your security team should do

• Immediately identify all NETGEAR ProSAFE Network Management System deployments and determine whether version 1.6.0.26 is in use.
• Treat vulnerable instances as high priority because the EPSS score is elevated and the flaw can disable a network management platform.
• Remove internet exposure and restrict administrative access to trusted networks, VPN, or bastion hosts.
• Upgrade to a vendor-fixed release if available; otherwise plan product replacement or decommissioning.
• Review recent web, proxy, WAF, and application logs for realName parameters containing path traversal sequences.
• Check for unexpected deletion or disappearance of application files, configuration files, logs, database files, or service binaries.
• Restore affected files from known-good backups if disruption is detected, then rebuild the host if system integrity cannot be trusted.
• Create SIEM detections for encoded and unencoded traversal attempts against NETGEAR ProSAFE NMS endpoints and parameters.