CVE-2025-21120 Overview
Dell Avamar contains an information exposure vulnerability caused by trusting HTTP permission methods on the server side. The flaw affects Dell Avamar and Dell Avamar Virtual Edition versions prior to 19.10 SP1 with patch 338904. A remote attacker with low privileges can exploit the weakness to access sensitive information from the Avamar server. The vulnerability is tracked under CWE-650: Trusting HTTP Permission Methods on the Server Side and was disclosed in Dell Security Advisory DSA-2025-271.
Critical Impact
Authenticated remote attackers can retrieve confidential data from Dell Avamar backup infrastructure by leveraging non-standard HTTP methods.
Affected Products
- Dell Avamar 19.4, 19.7, 19.8, 19.9 (Virtual Edition on ESXi, VMware, vSphere)
- Dell Avamar 19.10 and 19.10 SP1 prior to patch 338904
- Dell Avamar 19.12 prior to fixed release
Discovery Timeline
- 2025-08-04 - CVE CVE-2025-21120 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-21120
Vulnerability Analysis
Dell Avamar is an enterprise backup and recovery product widely deployed to protect virtualized workloads. The affected component exposes HTTP endpoints that enforce access control based on the HTTP method used in the request. The server trusts methods such as GET, POST, HEAD, or non-standard verbs to determine whether a security check applies. An attacker who submits requests using an unexpected method can bypass method-based restrictions and reach handlers that return sensitive data.
Because exploitation only impacts confidentiality, the flaw does not permit modification of backup data or denial of service. However, Avamar servers often contain metadata about backup clients, storage locations, and credentials-related configuration, which increases the sensitivity of any leaked information.
Root Cause
The root cause is improper reliance on HTTP verb filtering rather than uniform authorization checks on the resource handler. This weakness matches CWE-650, where developers assume that restricting a subset of HTTP methods is sufficient to protect a resource. Authorization logic tied to the request method rather than the resource itself allows equivalent operations under alternate verbs to bypass the intended controls.
Attack Vector
Exploitation requires network access to the Avamar management interface and valid low-privileged credentials. The attacker crafts HTTP requests using verbs the application does not restrict, targeting endpoints that would otherwise reject unauthorized access. No user interaction is required. Refer to DSA-2025-271 for vendor-specific technical detail.
Detection Methods for CVE-2025-21120
Indicators of Compromise
- HTTP requests to Avamar management endpoints using uncommon verbs such as HEAD, OPTIONS, TRACE, or arbitrary method strings.
- Successful 2xx responses to endpoints that normally require higher privileges when accessed with GET or POST.
- Repeated authenticated requests from a single low-privileged Avamar user account enumerating multiple URIs.
Detection Strategies
- Review Avamar web server access logs for anomalous HTTP method usage and correlate with the requesting user identity.
- Inspect authentication logs for low-privileged accounts issuing large volumes of API calls within short time windows.
- Deploy web application firewall rules that alert on non-standard HTTP verbs directed at Avamar management URIs.
Monitoring Recommendations
- Forward Avamar HTTP and audit logs to a centralized SIEM for cross-correlation with identity telemetry.
- Baseline normal HTTP method distribution for the Avamar management interface and alert on deviations.
- Monitor for unauthorized data export activity following anomalous request patterns.
How to Mitigate CVE-2025-21120
Immediate Actions Required
- Apply Dell Avamar patch 338904 on top of 19.10 SP1, or upgrade to a fixed release as directed in DSA-2025-271.
- Restrict network access to the Avamar management interface to trusted administrative networks only.
- Rotate credentials for low-privileged Avamar accounts and review recent access logs for suspicious activity.
Patch Information
Dell released the fix in patch 338904 for Dell Avamar and Dell Avamar Virtual Edition 19.10 SP1. Customers on earlier branches (19.4, 19.7, 19.8, 19.9) should upgrade to the fixed release. Full remediation guidance is provided in the Dell Security Update DSA-2025-271.
Workarounds
- Enforce network segmentation so only authorized administrator hosts can reach the Avamar HTTP interface.
- Deploy a reverse proxy or WAF in front of Avamar that rejects HTTP methods outside an approved allow list.
- Audit and reduce the number of accounts holding any level of Avamar access until patching is complete.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
