CVE-2017-8804 in C Library
Summary
by MITRE
The xdr_bytes and xdr_string functions in the GNU C Library (aka glibc or libc6) 2.25 mishandle failures of buffer deserialization, which allows remote attackers to cause a denial of service (virtual memory allocation, or memory consumption if an overcommit setting is not used) via a crafted UDP packet to port 111, a related issue to CVE-2017-8779.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2017-8804 resides within the GNU C Library implementation of the XDR (External Data Representation) functions, specifically affecting xdr_bytes and xdr_string operations in glibc version 2.25. This flaw manifests when the library processes buffer deserialization operations that fail during network packet handling, particularly when receiving crafted UDP packets on port 111 which is commonly used for the SunRPC (Remote Procedure Call) service. The issue stems from inadequate error handling during the deserialization process where the library fails to properly manage memory allocation failures that occur when processing malformed data structures. The vulnerability is classified under CWE-129 as an improper validation of array index, specifically manifesting in buffer over-read conditions during XDR processing. This weakness allows attackers to exploit the memory management behavior of the library, creating a path for denial of service attacks that can exhaust system resources through excessive virtual memory allocation or consume available memory when overcommit settings are disabled.
The technical exploitation of this vulnerability occurs through the manipulation of XDR data structures in RPC communications, where attackers craft specially formatted UDP packets that trigger memory allocation failures within the glibc library. When these malformed packets are processed by the xdr_bytes and xdr_string functions, the library's failure to properly handle the deserialization errors leads to uncontrolled memory consumption patterns. The vulnerability specifically impacts systems running glibc 2.25 and potentially other versions within the 2.25 release series, making it particularly concerning for network services that rely on RPC functionality for inter-process communication. The attack vector requires network access to port 111, which is commonly used by the portmapper service that facilitates RPC communication across network boundaries. This makes the vulnerability particularly dangerous in environments where RPC services are exposed to untrusted networks or where the portmapper service is running with default configurations that do not implement proper access controls.
The operational impact of CVE-2017-8804 extends beyond simple service disruption to potentially cause system instability and resource exhaustion that can affect overall system availability. When exploited, the vulnerability can cause the target system to allocate excessive amounts of virtual memory or consume available physical memory, leading to denial of service conditions that may require system restarts to resolve. The memory consumption patterns can vary significantly depending on system configurations, particularly the overcommit settings that determine how the kernel handles memory allocation requests. Systems with overcommit disabled are particularly vulnerable as they will fail more predictably when memory allocation limits are exceeded, while systems with overcommit enabled may experience gradual performance degradation before complete resource exhaustion. The vulnerability also has implications for network infrastructure services that rely on RPC functionality, including NIS (Network Information Service), NFS (Network File System), and other services that depend on proper XDR handling for data exchange. This makes the vulnerability particularly relevant for enterprise environments where these services are commonly deployed and maintained.
Mitigation strategies for CVE-2017-8804 focus primarily on updating the affected glibc library to patched versions that properly handle buffer deserialization failures. System administrators should prioritize applying security patches from their respective distribution vendors, as the vulnerability affects multiple Linux distributions that ship with glibc 2.25 or similar versions. Network-level mitigations include implementing firewall rules that restrict access to port 111 from untrusted networks, particularly for systems that do not require RPC services. The use of network segmentation and access control lists can help reduce the attack surface by limiting which systems can communicate with RPC services on port 111. Additionally, monitoring systems should be configured to detect unusual memory consumption patterns or network traffic patterns that might indicate exploitation attempts. Organizations should also consider disabling unnecessary RPC services and portmapper functionality when not required, as this reduces the potential attack surface for this and similar vulnerabilities. The ATT&CK framework categorizes this vulnerability under T1499.004 for network denial of service, with potential lateral movement implications through compromised RPC services that could be leveraged for further system compromise. Regular vulnerability assessments and security audits should include checking for affected glibc versions to ensure comprehensive protection against this and related memory handling vulnerabilities in the system's core libraries.