CVE-2021-3490 is a high-severity vulnerability affecting the Linux kernel, specifically related to the eBPF ALU32 bounds tracking for bitwise operations. This vulnerability allows for improper updates to 32-bit bounds, potentially leading to out-of-bounds reads and writes, which can result in arbitrary code execution. Given the potential impact, organizations should prioritize patching immediately.
The vulnerability has a CVSS score of 7.8, indicating a high severity level. This score reflects the significant risk posed to organizations that utilize affected versions of the Linux kernel. The exploitability of this vulnerability is also highlighted by its presence in known exploit databases and its classification as a high-priority issue by security advisories.
Organizations running the Linux kernel versions prior to the patched releases should take immediate action to mitigate the risk associated with this vulnerability. The urgency is accentuated by the fact that attackers may leverage this vulnerability for local privilege escalation, allowing them to gain elevated access to sensitive resources.
The vulnerability was published on June 4, 2021, and has since been addressed in kernel versions 5.12.4, 5.11.21, and 5.10.37, as well as the newer 5.13-rc4. Organizations must ensure that they are running these patched versions to protect against potential exploitation.
Vulnerability Details
The eBPF ALU32 bounds tracking for bitwise operations (AND, OR, and XOR) in the Linux kernel did not properly update 32-bit bounds, which could be turned into out-of-bounds reads and writes in the Linux kernel, leading to arbitrary code execution. This issue was fixed via commit 049c4e13714e ("bpf: Fix alu32 const subreg bound tracking on bitwise operations") (v5.13-rc4) and backported to the stable kernels in v5.12.4, v5.11.21, and v5.10.37.
The AND/OR issues were introduced by commit 3f50f132d840 ("bpf: Verifier, do explicit ALU32 bounds tracking") (5.7-rc1) and the XOR variant was introduced by commit 2921c90d4718 ("bpf: Fix a verifier failure with xor") (5.10-rc1).
Technical Analysis
The root cause of this vulnerability lies in the improper bounds tracking of 32-bit operations within the eBPF subsystem of the Linux kernel. Attackers can exploit this vulnerability through a local attack vector, where they can execute arbitrary code with low privileges. The attack complexity is classified as high, indicating that successful exploitation requires a sophisticated understanding of the underlying system.
The necessary privileges to exploit this vulnerability are low, meaning that an attacker could achieve exploitation with minimal access. User interaction is not required, which increases the risk as malicious actors can automate their attacks. The impacts on confidentiality, integrity, and availability are all classified as high, indicating a severe threat to affected systems.
Risk & Impact Analysis
Real-world deployment of the affected Linux kernel versions carries significant risk, particularly for organizations that rely on Linux for critical applications. The potential for arbitrary code execution means that attackers may gain unauthorized control over systems, leading to data breaches, service interruptions, or other malicious activities.
The blast radius of this vulnerability is considerable, as it can affect any system running the vulnerable versions of the Linux kernel. Organizations should assess their deployment strategies and ensure that systems are updated promptly to mitigate this risk.
Given the CVSS score of 7.8 and the presence of this vulnerability in the KEV catalog, organizations should address this issue in their priority patch cycle. The likelihood of exploitation, coupled with the high impact of a successful attack, underscores the urgency for remediation.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | Yes |
Public PoC | Yes |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The affected versions of the Linux kernel include all versions from 5.10 up to but not including 5.10.37, from 5.11 up to but not including 5.11.21, and from 5.12 up to but not including 5.12.4. Specific affected distributions include Ubuntu Linux versions 20.04, 20.10, and 21.04.
Mitigation & Remediation
To remediate this vulnerability, organizations should upgrade to patched versions of the Linux kernel. The recommended versions include 5.12.4, 5.11.21, and 5.10.37. If immediate patching is not feasible, organizations should consider applying workarounds and implementing configuration hardening measures to mitigate exposure.
Implementing network controls to limit local access to the systems running vulnerable kernel versions can also reduce the risk of exploitation. Continuous security testing should be performed to validate the effectiveness of the patch and to identify any potential weaknesses.
Organizations can benefit from engaging in services such as penetration testing to assess their security posture and identify any vulnerabilities that may remain unaddressed.
Detection Guidance
To detect potential exploitation, organizations should monitor logs for unusual behavior, particularly around system calls related to eBPF. Behavioral anomalies may include unexpected privilege escalation attempts or unauthorized access to critical system resources.
Network signatures for monitoring potential exploit attempts should also be established. Additionally, any changes to the system that deviate from the expected configuration should be closely monitored to identify potential exploitation of this vulnerability.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2021-3490 highlights the importance of rigorous security practices within the development and deployment of kernel components. This vulnerability represents a trend where complex subsystems in operating systems can introduce critical vulnerabilities if not properly managed.
Security teams should learn from this incident to implement better validation of bounds in kernel programming. Furthermore, they should conduct thorough reviews of kernel patches and updates to ensure that similar issues do not arise in the future.
For further reading on penetration testing methodologies and practices, organizations can refer to our guide on penetration testing methodology, as well as our discussions on vulnerability management programs and the importance of continuous security assessments.
Known Exploitation Timeline
This vulnerability is not currently listed as actively exploited in the KEV catalog, indicating that while it is important, there has been no confirmed evidence of widespread exploitation in the wild.
EPSS Risk Context
The EPSS score for CVE-2021-3490 is 0.054, placing it in the 90th percentile. This suggests a lower probability of exploitation compared to other vulnerabilities, but organizations should still remain vigilant and apply necessary patches.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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