CVE-2017-9951 in Memcached
Summary
by MITRE
The try_read_command function in memcached.c in memcached before 1.4.39 allows remote attackers to cause a denial of service (segmentation fault) via a request to add/set a key, which makes a comparison between signed and unsigned int and triggers a heap-based buffer over-read. NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-8705.
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Analysis
by VulDB Data Team • 12/13/2022
The vulnerability described in CVE-2017-9951 represents a critical denial of service flaw affecting memcached versions prior to 1.4.39. This issue manifests within the try_read_command function in memcached.c, where a fundamental programming error creates an exploitable condition that can be leveraged by remote attackers to crash the memcached daemon. The vulnerability specifically occurs when processing requests to add or set keys, making it particularly dangerous as it targets core operational functions of the caching system. The flaw stems from an incomplete fix for CVE-2016-8705, indicating a regression in the software's security posture that allows the original vulnerability to persist and potentially be exploited in new ways.
The technical root cause of this vulnerability lies in a dangerous comparison between signed and unsigned integers within the memory management logic of memcached. When a client sends a request to add or set a key, the system performs a comparison operation that mixes signed integer types with unsigned integer types, creating a condition where the program's memory access becomes unpredictable. This comparison error leads to a heap-based buffer over-read, where the application attempts to read memory beyond the allocated buffer boundaries. The over-read condition ultimately results in a segmentation fault that crashes the memcached process, effectively causing a denial of service that impacts all applications relying on the caching system.
The operational impact of CVE-2017-9951 extends beyond simple service disruption as it represents a significant threat to system availability and reliability in production environments. Organizations running vulnerable memcached instances face the risk of sustained denial of service attacks that can render their caching infrastructure completely unusable, potentially cascading into broader system failures. The vulnerability is particularly concerning because it requires no authentication to exploit, meaning any remote attacker can potentially compromise the service. This makes it a prime target for automated scanning and exploitation, especially in environments where memcached is exposed to untrusted networks or internet-facing services. The segmentation fault crash can also potentially expose underlying system information or create conditions that might allow for more sophisticated attacks if the system is not properly secured.
Mitigation strategies for CVE-2017-9951 should prioritize immediate patching of affected memcached installations to version 1.4.39 or later, which contains the proper fix for this vulnerability. Organizations should also implement network segmentation to limit access to memcached services, ensuring that only trusted internal systems can communicate with the caching infrastructure. Additional protective measures include configuring firewall rules to restrict access to memcached ports, implementing proper access controls and authentication mechanisms, and monitoring for unusual patterns of requests that might indicate exploitation attempts. The vulnerability aligns with CWE-191, which specifically addresses unsigned integer underflow conditions, and relates to ATT&CK technique T1499.004 for network denial of service attacks. Security teams should also consider implementing intrusion detection systems to monitor for exploitation attempts and maintain comprehensive backup and recovery procedures to quickly restore services if attacks occur.