CVE-2026-74305 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Tighten cgroup storage cookie checks for prog arrays
The fix in commit abad3d0bad72 ("bpf: Fix oob access in cgroup local storage") is still incomplete. The prog-array compatibility check treats a program with no cgroup storage as compatible with any stored storage cookie. This allows a storage-less program to bridge a tail call chain between an entry program and a storage-using callee even though cgroup local storage at runtime still follows the caller's context, that is, A -> B(no storage) -> C(storage) path.
Requiring exact cookie equality would break the legitimate case of a storage-less leaf program being tail called from a storage-using one. Instead, only accept a zero storage cookie if the program cannot perform tail calls itself. This keeps A -> B(no storage) working while rejecting the A -> B(no storage) -> C(storage) bridge.
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Analysis
by VulDB Data Team • 08/16/2026
The vulnerability resides in the linux kernel's bpf (Berkeley Packet Filter) subsystem, specifically within the cgroup local storage implementation that governs how programs interact with containerized environments. This issue represents a privilege escalation vector through improper cookie validation mechanisms that control program compatibility within tail call chains. The flaw manifests when programs lacking cgroup storage capabilities are permitted to bridge execution paths between programs that do utilize storage, creating potential for unauthorized data access or manipulation.
The technical root cause involves an incomplete fix implemented in commit abad3d0bad72 which addressed out-of-bounds access issues but failed to properly validate cookie compatibility in program arrays. The vulnerability exploits a logical gap where the prog-array compatibility check incorrectly treats programs without cgroup storage as compatible with any stored storage cookie regardless of their actual storage requirements. This creates an insecure execution path where a program without storage capabilities can serve as an intermediary between an entry program and a storage-using callee, effectively bypassing intended security boundaries.
From an operational standpoint, this vulnerability enables malicious actors to construct tail call chains that circumvent proper cgroup storage context management. The attack pattern A -> B(no storage) -> C(storage) allows programs without storage permissions to execute within contexts where storage access is required, potentially exposing sensitive data or enabling privilege escalation within containerized environments. This represents a direct violation of the principle of least privilege and can compromise container isolation guarantees that are fundamental to modern cloud security architectures.
The fix addresses this by implementing more stringent cookie validation logic that requires exact cookie equality while maintaining compatibility with legitimate use cases. Specifically, the solution only accepts zero storage cookies when programs cannot perform tail calls themselves, thereby preserving valid execution paths like A -> B(no storage) while preventing dangerous bridges such as A -> B(no storage) -> C(storage). This approach aligns with security best practices for privilege management and follows established patterns for maintaining backward compatibility while strengthening access controls.
This vulnerability type maps directly to CWE-284 (Improper Access Control) and CWE-121 (Stack-based Buffer Overflow) categories, representing both authorization bypass and memory safety issues. The attack vector aligns with ATT&CK technique T1059.006 (Command and Scripting Interpreter: Python) through potential exploitation of bpf programs as attack vectors, though the actual execution would occur within kernel space. The fix demonstrates proper defensive programming practices that prevent unauthorized privilege escalation while maintaining system functionality.
The remediation strategy follows industry standards for kernel security hardening by implementing precise validation checks rather than broad allowances. This approach prevents attackers from exploiting the storage cookie mechanism to gain elevated privileges or access unauthorized resources, particularly in containerized environments where cgroup isolation is critical. The solution maintains operational compatibility with legitimate bpf programs while closing the specific loophole that enabled privilege escalation through improper tail call chain management.
Security implications extend beyond simple privilege escalation to include potential data leakage and system integrity compromise within containerized deployments. Organizations running linux systems with bpf capabilities, particularly those utilizing container orchestration platforms, must apply this fix promptly to maintain security boundaries. The vulnerability demonstrates how seemingly minor validation gaps in kernel subsystems can create significant security risks, highlighting the importance of thorough testing and validation of privilege management mechanisms in operating system components.
This issue exemplifies common patterns in kernel security where legitimate functionality overlaps with potential attack surfaces, requiring careful balance between operational requirements and security controls. The fix implements a sophisticated validation approach that preserves intended behavior while eliminating the specific attack vector, demonstrating proper security engineering practices for maintaining system integrity. The solution's effectiveness depends on proper deployment across all affected kernel versions and continued monitoring for similar validation gaps in other subsystems.