CVE-2021-21510: Dell iDRAC8 Host Header Injection Flaw

CVE-2021-21510 Overview

Dell iDRAC8 versions prior to 2.75.100.75 contain a host header injection vulnerability. A remote unauthenticated attacker may potentially exploit this vulnerability by injecting arbitrary 'Host' header values to poison a web-cache or trigger redirections. This vulnerability falls under the category of improper input validation (CWE-20) and injection flaws (CWE-74).

Critical Impact

Unauthenticated attackers can manipulate HTTP Host headers to poison web caches or redirect users to malicious sites, potentially enabling phishing attacks or session hijacking against administrators managing server infrastructure through iDRAC8.

Affected Products

• Dell iDRAC8 Firmware versions prior to 2.75.100.75

Discovery Timeline

• 2021-03-08 - CVE-2021-21510 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-21510

Vulnerability Analysis

The vulnerability exists in how Dell iDRAC8 firmware handles HTTP Host header values in incoming requests. The web interface fails to properly validate or sanitize the Host header, allowing attackers to inject arbitrary values. This design flaw enables two primary attack scenarios: web cache poisoning and open redirect attacks.

In a web cache poisoning scenario, an attacker can craft requests with manipulated Host headers that, when cached by intermediary proxies or CDNs, serve malicious content to legitimate users. For redirect attacks, the injected Host header values can cause the iDRAC8 interface to generate redirects pointing to attacker-controlled domains.

The attack is particularly concerning because iDRAC8 (Integrated Dell Remote Access Controller) is used for out-of-band server management, giving administrators remote access to critical server hardware. Compromising this interface could lead to broader infrastructure attacks.

Root Cause

The root cause is improper input validation (CWE-20) combined with injection vulnerabilities (CWE-74) in the iDRAC8 web server component. The firmware does not validate that the HTTP Host header matches expected values or sanitize special characters before using the header value in response generation. This allows attackers to inject arbitrary content that gets reflected in HTTP responses.

Attack Vector

The attack is network-based and requires no authentication or special privileges, though user interaction is required for successful exploitation. An attacker must craft malicious HTTP requests with poisoned Host header values and send them to the iDRAC8 web interface. The vulnerability can be exploited by:

1. Sending crafted HTTP requests with malicious Host header values to the iDRAC8 interface
2. If caching infrastructure exists between users and iDRAC8, poisoned responses may be cached and served to other users
3. Manipulated Host headers can cause the server to generate redirect responses pointing to attacker-controlled domains
4. Victims following these redirects could be directed to phishing pages mimicking the iDRAC login interface

The vulnerability mechanism involves improper handling of HTTP Host headers in the iDRAC8 web server. When processing HTTP requests, the server uses the Host header value without adequate validation, allowing attackers to inject arbitrary values that are reflected in server responses. For detailed technical information, refer to the Dell EMC Security Update.

Detection Methods for CVE-2021-21510

Indicators of Compromise

• HTTP requests to iDRAC8 interfaces containing unusual or malformed Host header values
• Web server logs showing requests with Host headers that don't match the expected iDRAC8 hostname or IP address
• Unexpected redirect responses from iDRAC8 pointing to external domains
• Reports of users being redirected to suspicious login pages when accessing iDRAC interfaces

Detection Strategies

• Monitor HTTP access logs for requests containing Host headers that don't match configured iDRAC8 hostnames
• Implement web application firewalls (WAF) to detect and block requests with suspicious Host header manipulation patterns
• Review proxy and cache logs for cached responses with unexpected Host header values or redirect destinations
• Deploy network-based intrusion detection signatures to identify Host header injection attempts targeting iDRAC8 endpoints

Monitoring Recommendations

• Enable comprehensive HTTP request logging on iDRAC8 interfaces and forward logs to SIEM for analysis
• Configure alerts for any HTTP redirect responses from iDRAC8 that point to external or unexpected domains
• Monitor for anomalous patterns in iDRAC8 web interface access, particularly from unexpected source IPs
• Implement periodic firmware version audits to ensure all iDRAC8 instances are running patched firmware versions

How to Mitigate CVE-2021-21510

Immediate Actions Required

• Upgrade Dell iDRAC8 firmware to version 2.75.100.75 or later immediately
• Restrict network access to iDRAC8 interfaces to trusted management networks only
• Implement network segmentation to isolate iDRAC/out-of-band management interfaces from general user traffic
• Review web server and proxy logs for signs of past exploitation attempts

Patch Information

Dell has released firmware version 2.75.100.75 to address this vulnerability. Administrators should download and apply the security update from Dell's official support channels. For complete details and download links, refer to the Dell EMC Security Advisory DSA-2021-041.

Workarounds

• Restrict iDRAC8 access to dedicated management VLANs with strict access control lists
• Place a reverse proxy with Host header validation in front of iDRAC8 interfaces
• Disable or limit caching for iDRAC8 web interface traffic if proxies are in use
• Implement network access controls to ensure only authorized administrators can reach iDRAC8 interfaces

# Example: Restrict iDRAC8 access using iptables (on network firewall)
# Allow only trusted management subnet to access iDRAC8 on HTTPS port
iptables -A INPUT -p tcp --dport 443 -s 10.0.10.0/24 -d <idrac_ip> -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -d <idrac_ip> -j DROP