CVE-2026-68458 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
binder: cache secctx size before release zeroes it
binder_transaction() bounds the scatter-gather buffer area with sg_buf_end_offset and subtracts the aligned LSM context size because the secctx is written at the tail of that area. The subtraction reads lsmctx.len, but that field has already been cleared by the time the line runs:
security_secid_to_secctx(secid, &lsmctx) /* lsmctx.len set */ lsmctx_aligned_size = ALIGN(lsmctx.len, sizeof(u64)) extra_buffers_size += lsmctx_aligned_size ... security_release_secctx(&lsmctx) /* memset zeroes len */ ... sg_buf_end_offset = sg_buf_offset + extra_buffers_size - ALIGN(lsmctx.len, sizeof(u64)) /* ALIGN(0,8) */
security_release_secctx() does memset(cp, 0, sizeof(*cp)), so lsmctx.len reads back as 0 and the subtraction contributes nothing, leaving sg_buf_end_offset too large by the aligned secctx size on every transaction to a txn_security_ctx node.
Each BINDER_TYPE_PTR object then derives buf_left = sg_buf_end_offset - sg_buf_offset as the sole upper bound on its copy, so the inflated end offset lets the copy run into the bytes that already hold the secctx.
The aligned size must therefore be cached before release rather than re-read from the now-cleared field. Fix by caching it in lsmctx_aligned_size at function scope when it is first computed and subtracting lsmctx_aligned_size instead of re-reading lsmctx.len after release. Reuse the same value for the earlier buf_offset computation.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described involves a critical flaw in the Linux kernel's binder driver that handles inter-process communication between Android applications and system services. This issue specifically affects how the kernel manages security context information during transaction processing, creating a potential memory corruption scenario that could be exploited by malicious actors. The problem manifests when the binder subsystem processes transactions that involve security contexts, particularly those involving LSM (Linux Security Module) security labels.
The core technical flaw occurs in the binder_transaction() function where the kernel attempts to calculate buffer boundaries for scatter-gather operations while accounting for security context storage. The system first retrieves the security context using security_secid_to_secctx() which populates the lsmctx.len field with the actual size of the security context data. However, immediately after this operation, the kernel calls security_release_secctx() which performs a memset operation on the entire structure, effectively zeroing out the lsmctx.len field. When the code later attempts to calculate the aligned security context size by re-reading lsmctx.len, it retrieves a value of zero instead of the previously calculated size.
This fundamental timing issue results in incorrect buffer boundary calculations where the sg_buf_end_offset is computed to be larger than necessary by exactly the amount of the aligned security context size. The miscalculated offset causes subsequent copy operations to extend beyond their intended boundaries and overwrite memory regions that already contain valid security context data. This creates a classic buffer overflow condition that could potentially allow privilege escalation or denial of service attacks.
The operational impact extends beyond simple memory corruption as the vulnerability affects all binder transactions involving security contexts, which are common in Android's system services and application communication mechanisms. The flaw is particularly concerning because it operates at the kernel level and affects the fundamental inter-process communication infrastructure that underpins Android's security model. According to CWE classification, this represents a CWE-121: Stack-based Buffer Overflow, while the ATT&CK framework would categorize this as a privilege escalation technique through kernel memory corruption.
The fix implemented addresses the root cause by caching the aligned security context size at function scope before the security_release_secctx() call occurs. This approach ensures that the calculated value remains available for both the buffer boundary calculation and the earlier buf_offset computation, eliminating the race condition between the security context population and its subsequent zeroing. The solution maintains the same functional behavior while preventing the memory corruption by ensuring consistent size calculations throughout the transaction processing flow. This mitigation aligns with secure coding practices that emphasize avoiding reliance on values that may be modified during execution sequences.
The vulnerability demonstrates how seemingly simple operations in kernel code can create complex security issues when timing dependencies are not properly considered, particularly in systems that manage security contexts and memory boundaries simultaneously. The fix represents a straightforward but critical correction to the order of operations that prevents the accidental reuse of zeroed data in buffer calculations, thereby preserving the integrity of the binder driver's memory management and maintaining the security boundaries that protect Android applications from unauthorized access or manipulation.