CVE-2017-7618 in Linux
Summary
by MITRE • 01/25/2023
crypto/ahash.c in the Linux kernel through 4.10.9 allows attackers to cause a denial of service (API operation calling its own callback, and infinite recursion) by triggering EBUSY on a full queue.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2017-7618 resides within the Linux kernel's cryptographic subsystem, specifically in the crypto/ahash.c file. This flaw represents a critical design issue that can be exploited to trigger a denial of service condition through carefully crafted API operations. The vulnerability affects Linux kernel versions through 4.10.9, making it a widespread concern across numerous production systems. The core issue manifests when an attacker can manipulate the kernel's asynchronous hash operation handling to create a scenario where an API operation calls its own callback function recursively, leading to infinite recursion and system instability.
The technical implementation of this vulnerability stems from improper handling of error conditions within the asynchronous hash algorithm framework. When the kernel's cryptographic queue reaches capacity and returns an EBUSY error code, the callback mechanism fails to properly handle this condition. Instead of gracefully managing the overflow or implementing proper queue management, the system enters a recursive loop where the same callback function repeatedly invokes itself. This recursive behavior occurs because the error handling logic does not properly distinguish between legitimate operation failures and conditions that should trigger a restart or retry mechanism. The flaw essentially creates a self-referential loop within the kernel's cryptographic processing pipeline, where the error condition itself becomes the catalyst for continued execution of the problematic code path.
The operational impact of CVE-2017-7618 extends beyond simple system unresponsiveness to potentially catastrophic system failure scenarios. When exploited successfully, this vulnerability can cause complete system hangs or forced reboots, effectively rendering affected systems unavailable to legitimate users and applications. The infinite recursion consumes CPU cycles continuously without producing any meaningful cryptographic output, leading to resource exhaustion that can affect other kernel subsystems and overall system performance. In high-availability environments or mission-critical systems, this vulnerability could result in extended downtime and service disruption that impacts business operations significantly. The vulnerability is particularly concerning because it operates at the kernel level, making it difficult to detect and mitigate without system-level intervention.
This vulnerability aligns with CWE-691, which describes insufficient control flow management in software systems. The recursive callback behavior demonstrates poor error handling practices that violate fundamental principles of secure programming. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, as it can be leveraged to create persistent system unavailability. The flaw also connects to T1070.006, which covers credential dumping and system information gathering, as attackers may use this vulnerability as a preliminary step to gain system control. Mitigation strategies should include kernel updates to versions that address this specific recursion issue in the cryptographic subsystem, implementing proper queue management mechanisms, and establishing monitoring systems to detect unusual callback behavior patterns. Organizations should also consider implementing kernel hardening measures and ensuring that cryptographic operations properly handle error conditions without entering recursive execution paths, as outlined in the NIST SP 800-53 security controls for operating systems and kernel integrity protection.