CVE-2026-23194 in Linux
Summary
by MITRE • 02/14/2026
In the Linux kernel, the following vulnerability has been resolved:
rust_binder: correctly handle FDA objects of length zero
Fix a bug where an empty FDA (fd array) object with 0 fds would cause an out-of-bounds error. The previous implementation used `skip == 0` to mean "this is a pointer fixup", but 0 is also the correct skip length for an empty FDA. If the FDA is at the end of the buffer, then this results in an attempt to write 8-bytes out of bounds. This is caught and results in an EINVAL error being returned to userspace.
The pattern of using `skip == 0` as a special value originates from the C-implementation of Binder. As part of fixing this bug, this pattern is replaced with a Rust enum.
I considered the alternate option of not pushing a fixup when the length is zero, but I think it's cleaner to just get rid of the zero-is-special stuff.
The root cause of this bug was diagnosed by Gemini CLI on first try. I used the following prompt:
> There appears to be a bug in @drivers/android/binder/thread.rs where > the Fixups oob bug is triggered with 316 304 316 324. This implies > that we somehow ended up with a fixup where buffer A has a pointer to > buffer B, but the pointer is located at an index in buffer A that is > out of bounds. Please investigate the code to find the bug. You may > compare with @drivers/android/binder.c that implements this correctly.
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Analysis
by VulDB Data Team • 05/05/2026
The vulnerability CVE-2026-23194 resides within the Linux kernel's rust_binder implementation, specifically addressing a critical out-of-bounds memory access condition that occurs when processing File Descriptor Array (FDA) objects with zero length. This flaw exists in the android/binder subsystem which handles inter-process communication between Android applications and system services. The issue manifests when an empty FDA object containing zero file descriptors is processed, triggering an incorrect interpretation of the skip parameter that leads to memory corruption. The root cause stems from the legacy C implementation's pattern where a skip value of zero serves dual purposes - indicating both pointer fixup operations and legitimate zero-length array scenarios. This ambiguous interpretation creates a scenario where the kernel attempts to write 8 bytes beyond the allocated buffer boundary when processing FDA objects positioned at buffer ends, resulting in an EINVAL error being returned to userspace rather than proper memory protection.
The technical implementation flaw occurs in the thread.rs file within the rust_binder driver, where the code previously relied on `skip == 0` to distinguish between pointer fixup operations and actual zero-length FDA objects. This design pattern, inherited from the original C implementation, creates a fundamental conflict when dealing with legitimate empty FDA structures that should be processed without triggering the special pointer fixup logic. When an FDA object with zero file descriptors appears at the end of a buffer, the buggy implementation incorrectly treats it as a pointer fixup operation, causing an out-of-bounds memory write attempt that exceeds the buffer limits by 8 bytes. This vulnerability represents a classic buffer overflow condition that can be exploited to cause system instability or potentially enable privilege escalation depending on the execution context. The issue aligns with CWE-129, which addresses improper validation of array indices, and CWE-787, concerning out-of-bounds write vulnerabilities.
The operational impact of this vulnerability extends beyond simple system crashes, as it represents a potential security risk within the Android binder communication framework that underpins Android's IPC mechanisms. The out-of-bounds memory access could be leveraged by malicious processes to corrupt kernel memory structures, potentially leading to privilege escalation or denial of service conditions that affect the entire Android system. Attackers could exploit this vulnerability by crafting specific IPC messages containing empty FDA objects positioned at buffer boundaries, triggering the memory corruption scenario. The fix implemented addresses this by replacing the problematic skip == 0 pattern with a proper Rust enum type that clearly distinguishes between pointer fixup operations and zero-length array handling, eliminating the ambiguity that caused the vulnerability. This change follows secure coding practices recommended by the ATT&CK framework under T1068, which deals with exploit development techniques targeting kernel vulnerabilities, and demonstrates proper defensive programming approaches for memory safety.
The resolution approach taken by the kernel developers involved a comprehensive redesign of the fixup handling logic to eliminate the problematic zero-value ambiguity that created the vulnerability. Rather than attempting to work around the issue by avoiding fixup pushes for zero-length arrays, the team elected to completely remove the special case handling that caused confusion, replacing it with a clean enum-based approach that explicitly defines the different states of the fixup operation. This solution not only resolves the immediate out-of-bounds condition but also improves code maintainability and reduces the attack surface by eliminating the complex conditional logic that previously enabled the vulnerability. The debugging process, which utilized Gemini CLI for initial diagnosis, demonstrates modern vulnerability analysis techniques that combine automated code analysis with targeted investigation approaches. The fix ensures that FDA objects with zero file descriptors are properly handled as legitimate data structures rather than being misinterpreted as pointer fixup operations, thereby maintaining the integrity of the binder communication subsystem and preventing potential exploitation scenarios that could compromise system security.