CVE-2021-33033 in Linux
Summary
by MITRE • 05/15/2021
The Linux kernel before 5.11.14 has a use-after-free in cipso_v4_genopt in net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting for the DOI definitions is mishandled, aka CID-ad5d07f4a9cd. This leads to writing an arbitrary value.
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Analysis
by VulDB Data Team • 05/16/2021
The vulnerability identified as CVE-2021-33033 represents a critical use-after-free condition within the Linux kernel's Common IP Security Option (CIPSO) implementation, specifically affecting versions prior to 5.11.14. This flaw exists in the cipso_v4_genopt function located in net/ipv4/cipso_ipv4.c, where improper reference counting mechanisms for CIPSO and CALIPSO DOI (Domain of Interpretation) definitions create a scenario where freed memory can be accessed and manipulated by malicious actors. The issue stems from inadequate management of reference counts for these security protocol definitions, allowing attackers to exploit the race condition that occurs during the refcounting process.
The technical exploitation of this vulnerability occurs through a sophisticated manipulation of the kernel's memory management system where the CIPSO and CALIPSO protocols maintain reference counts to track active usage of DOI definitions. When the kernel processes these security options, the improper handling of reference counting leads to a situation where memory allocated for DOI definitions is freed while still being referenced by other components. This creates a use-after-free condition where subsequent operations on the freed memory can be controlled by an attacker to write arbitrary values, potentially leading to privilege escalation or system compromise. The vulnerability manifests as a direct consequence of CWE-416, which specifically addresses use-after-free conditions in software systems.
The operational impact of CVE-2021-33033 extends beyond simple memory corruption, presenting significant security risks to systems running vulnerable Linux kernels. Attackers who successfully exploit this vulnerability can leverage the arbitrary write capability to manipulate kernel memory structures, potentially gaining elevated privileges or causing system instability. The vulnerability affects network security implementations that rely on CIPSO and CALIPSO protocols for IP security options, particularly in environments where these protocols are actively used for network access control or security policy enforcement. This weakness can be exploited in various attack scenarios including privilege escalation, denial of service, and potentially full system compromise, making it a high-severity issue for organizations maintaining Linux-based infrastructure.
Mitigation strategies for this vulnerability primarily focus on immediate kernel updates to versions 5.11.14 or later where the reference counting implementation has been corrected. System administrators should prioritize patching affected systems, particularly those running kernel versions between 5.11.0 and 5.11.13, as these versions are most susceptible to exploitation. Additionally, network administrators should implement monitoring for unusual network traffic patterns that might indicate exploitation attempts, as the vulnerability can be triggered through malformed CIPSO or CALIPSO packets. The fix addresses the underlying reference counting logic by ensuring proper synchronization and memory management when handling DOI definitions, preventing the race condition that leads to the use-after-free scenario. Organizations should also consider implementing network segmentation and access controls to limit exposure while patches are deployed, as the vulnerability can be exploited remotely through network-based attacks that leverage the CIPSO and CALIPSO protocol implementations.