CVE-2016-0798 in OpenSSL
Summary
by MITRE
Memory leak in the SRP_VBASE_get_by_user implementation in OpenSSL 1.0.1 before 1.0.1s and 1.0.2 before 1.0.2g allows remote attackers to cause a denial of service (memory consumption) by providing an invalid username in a connection attempt, related to apps/s_server.c and crypto/srp/srp_vfy.c.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2016-0798 represents a critical memory leak flaw within OpenSSL's implementation of the Secure Remote Password (SRP) protocol. This issue affects OpenSSL versions 1.0.1 through 1.0.1r and 1.0.2 through 1.0.2f, creating a persistent memory consumption problem that can be exploited remotely. The vulnerability specifically resides in the SRP_VBASE_get_by_user function located in the OpenSSL codebase, which is responsible for retrieving SRP user credentials during authentication processes. The flaw manifests when the system processes invalid usernames provided during connection attempts, leading to improper memory management and gradual resource exhaustion.
The technical implementation of this vulnerability stems from inadequate memory deallocation within the SRP_VBASE_get_by_user function in the apps/s_server.c and crypto/srp/srp_vfy.c files. When a remote attacker submits an invalid username during an SRP authentication attempt, the function fails to properly release allocated memory resources, causing memory fragments to accumulate over time. This memory leak occurs because the code path does not include proper cleanup routines for invalid user scenarios, particularly when the SRP verification process encounters malformed or non-existent usernames. The vulnerability follows the CWE-401 weakness category, which specifically addresses improper release of memory resources, making it a classic example of memory management failure in cryptographic implementations.
The operational impact of this vulnerability extends beyond simple resource exhaustion, creating significant denial of service conditions that can severely compromise system availability. Attackers can repeatedly submit invalid usernames to consume system memory resources, eventually causing the target server to become unresponsive or crash entirely. This memory consumption pattern can be particularly devastating in high-traffic environments where multiple concurrent connection attempts are common, as the memory leak compounds rapidly. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion, making it a direct threat to system availability and service integrity. The cumulative effect of this vulnerability can result in complete service disruption, requiring system restarts to restore normal operations.
Mitigation strategies for CVE-2016-0798 involve immediate patching of affected OpenSSL installations to versions 1.0.1s or 1.0.2g and later, which contain the necessary memory management fixes. Organizations should implement connection rate limiting and authentication attempt monitoring to detect and prevent abuse of this vulnerability. Network segmentation and access control measures can help limit the exposure of vulnerable systems to external attackers. Additionally, regular security audits should verify that all OpenSSL implementations are properly updated and that memory management practices are consistently applied across cryptographic components. The fix implemented in the patched versions ensures proper memory deallocation for invalid username scenarios, preventing the accumulation of memory fragments that previously led to system instability and service disruption.