CVE-2011-1076 in Linux
Summary
by MITRE
net/dns_resolver/dns_key.c in the Linux kernel before 2.6.38 allows remote DNS servers to cause a denial of service (NULL pointer dereference and OOPS) by not providing a valid response to a DNS query, as demonstrated by an erroneous grand.centrall.org query, which triggers improper handling of error data within a DNS resolver key.
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Analysis
by VulDB Data Team • 11/23/2021
The vulnerability identified as CVE-2011-1076 resides within the Linux kernel's DNS resolver implementation, specifically in the net/dns_resolver/dns_key.c file. This flaw represents a classic denial of service vulnerability that exploits improper error handling mechanisms within the kernel's networking stack. The vulnerability affects Linux kernel versions prior to 2.6.38 and demonstrates how malformed DNS responses can be leveraged to crash kernel processes. The issue manifests when remote DNS servers fail to provide valid responses to DNS queries, creating a scenario where the kernel's DNS resolver encounters error data that it cannot properly process. This particular vulnerability was demonstrated through an erroneous query to the grand.centrall.org domain, which triggered the specific code path that leads to system instability. The root cause of this vulnerability aligns with CWE-476, which describes NULL pointer dereferences, as the kernel fails to properly validate DNS response data before attempting to process it. This flaw exists in the kernel's DNS key management subsystem, where the resolver attempts to handle error conditions without adequate safeguards against malformed or incomplete responses.
The technical exploitation of this vulnerability occurs when a DNS resolver encounters a response that lacks proper data structure validation. When a remote DNS server fails to respond appropriately to a query, the kernel's DNS resolver code path attempts to process what it perceives as an error condition but lacks proper null checks before dereferencing pointers. This results in a NULL pointer dereference that ultimately causes an OOPS condition within the kernel, effectively crashing the system or rendering it unresponsive. The operational impact extends beyond simple denial of service, as this vulnerability can be exploited by remote attackers to disrupt network services without requiring authentication or elevated privileges. The vulnerability operates at the kernel level, making it particularly dangerous as it can affect system stability regardless of user permissions or application-level protections. The DNS resolver's failure to properly handle error responses creates a condition where legitimate network operations can be disrupted by simply sending malformed DNS responses, making this a particularly concerning vulnerability for network infrastructure components that rely heavily on DNS resolution.
The broader implications of CVE-2011-1076 extend to various network security scenarios where DNS resolution is critical for system operations. This vulnerability aligns with ATT&CK technique T1498, which describes network denial of service attacks, as it allows remote attackers to cause system unavailability through DNS response manipulation. Organizations utilizing Linux systems with kernel versions prior to 2.6.38 face significant risk from this vulnerability, as it can be exploited to disrupt services without requiring advanced attack capabilities. The vulnerability's impact is particularly severe in environments where DNS resolution is critical for system functionality, such as web servers, mail servers, and network infrastructure devices. System administrators should consider this vulnerability as part of their broader security posture assessment, particularly in environments where external DNS servers cannot be fully trusted. The flaw demonstrates the importance of robust error handling in kernel-level code and highlights how seemingly minor implementation issues can lead to significant system instability. Mitigation strategies must include kernel updates to version 2.6.38 or later, along with network-level protections that can filter or rate-limit DNS responses to prevent exploitation. Organizations should also implement monitoring to detect unusual DNS resolution patterns that might indicate attempted exploitation of this vulnerability, as the OOPS condition can be difficult to distinguish from other system failures without proper logging and alerting mechanisms.