CVE-2017-8831 in Linux
Summary
by MITRE
The saa7164_bus_get function in drivers/media/pci/saa7164/saa7164-bus.c in the Linux kernel through 4.10.14 allows local users to cause a denial of service (out-of-bounds array access) or possibly have unspecified other impact by changing a certain sequence-number value, aka a "double fetch" vulnerability.
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Analysis
by VulDB Data Team • 12/06/2022
The CVE-2017-8831 vulnerability resides within the Linux kernel's saa7164 driver subsystem, specifically in the saa7164_bus_get function located at drivers/media/pci/saa7164/saa7164-bus.c. This flaw represents a critical double fetch vulnerability that affects kernel versions through 4.10.14, enabling local attackers to manipulate sequence-number values and trigger unintended behavior. The vulnerability manifests when the function processes certain sequence-number inputs without proper validation, creating a scenario where the same variable is accessed twice in different contexts, leading to unpredictable outcomes. Such vulnerabilities are particularly dangerous in kernel space as they can be exploited to cause system instability or potentially escalate privileges.
The technical exploitation of this vulnerability occurs through a classic double fetch pattern where an attacker manipulates a sequence-number value that gets fetched twice during function execution. The first fetch operation retrieves the value, but subsequent processing or validation based on this value creates a window where the original value may have changed or been corrupted. This leads to out-of-bounds array access when the second fetch is used to index into an array, potentially causing memory corruption or system crashes. The vulnerability aligns with CWE-129, which describes improper validation of array indices, and specifically relates to the broader category of buffer overflow conditions that can result from inadequate input validation. The double fetch mechanism creates a race condition or state inconsistency that undermines the integrity of the validation process.
From an operational perspective, this vulnerability presents a significant risk to systems running affected Linux kernel versions, particularly those utilizing the saa7164 video capture hardware drivers. Local users can leverage this flaw to either cause a denial of service through system crashes or potentially achieve more severe impacts including privilege escalation. The impact extends beyond simple system instability as the vulnerability could be chained with other exploits to create more sophisticated attack vectors. The saa7164 driver is commonly used in digital television and video capture applications, meaning that systems in production environments with these drivers installed are at risk. Security analysts should note the potential for this vulnerability to be exploited in embedded systems or industrial control environments where kernel-level access is not properly restricted.
Mitigation strategies for CVE-2017-8831 involve immediate kernel updates to versions that contain the patched implementation of the saa7164_bus_get function. System administrators should prioritize applying the official kernel patches from their distribution vendors or directly from the Linux kernel source repository. Additionally, implementing proper input validation and bounds checking in kernel modules can help prevent similar vulnerabilities from manifesting in other driver components. The ATT&CK framework categorizes this type of vulnerability under privilege escalation techniques, specifically in the context of kernel exploits where local users can leverage memory corruption vulnerabilities to gain elevated privileges. Organizations should also consider implementing monitoring solutions to detect anomalous sequence-number patterns that might indicate exploitation attempts, while maintaining current threat intelligence feeds to stay informed about similar vulnerabilities in kernel subsystems.