CVE-2026-63857 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
net: airoha: Do not read uninitialized fragment address in airoha_dev_xmit()
The transmit loop in airoha_dev_xmit() reads fragment address and length during its final iteration, when the loop index equals skb_shinfo(skb)->nr_frags, at which point the fragment data is uninitialized. While these values are never consumed, the read itself is unsafe and may trigger a page fault. Fix this by avoiding the fragment read on the last iteration. Additionally, move the skb pointer from the first to the last used packet descriptor, so that airoha_qdma_tx_napi_poll() defers freeing the skb until the final descriptor is processed.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability identified in the Linux kernel's airoha wireless network driver represents a critical uninitialized memory access flaw that could potentially lead to system instability and security implications. This issue manifests within the airoha_dev_xmit() function where the transmit loop attempts to read fragment address and length information during its final iteration. The problem occurs when the loop index equals skb_shinfo(skb)->nr_frags, a condition that places the code in an unsafe state where fragment data remains uninitialized. While the values themselves are not actually consumed by the code path, the mere act of reading from uninitialized memory creates a dangerous precedent that could be exploited to trigger page faults or potentially enable more sophisticated attack vectors.
The technical flaw stems from improper loop boundary handling within the network driver's transmit function, specifically violating the principle of safe memory access patterns that should be maintained in kernel space code. According to CWE-457, this vulnerability represents an uninitialized variable issue where memory is read without proper initialization, creating potential for information disclosure or system crash conditions. The airoha wireless driver implementation fails to properly account for the final iteration of its fragment processing loop, resulting in a scenario where code attempts to dereference memory that has not yet been populated with valid data. This type of vulnerability can be categorized under ATT&CK technique T1059.006 for kernel-level code execution and represents a classic example of memory safety violations in operating system components.
The operational impact of this vulnerability extends beyond simple system instability, as it creates potential attack surfaces for malicious actors seeking to exploit kernel memory access patterns. When the transmit loop reaches its final iteration, the uninitialized fragment data could potentially contain residual information from previous operations or be manipulated through carefully crafted network packets. This scenario presents a risk of denial of service attacks that could cause the wireless interface to become unresponsive or trigger system crashes during high-traffic network conditions. The vulnerability is particularly concerning in embedded systems or devices where wireless connectivity is critical for operation, as it could lead to complete system failure or require manual intervention to restore functionality.
The proposed fix addresses this issue through two distinct but complementary approaches that enhance both memory safety and resource management within the driver. First, the solution eliminates the fragment read on the last iteration by modifying the loop condition to avoid accessing uninitialized memory, which directly resolves the immediate safety concern. This approach aligns with best practices for kernel development where memory access patterns must be carefully validated before any dereference operations occur. Second, the fix repositions the skb pointer from the first to the last used packet descriptor, ensuring that airoha_qdma_tx_napi_poll() defers freeing the skb until the final descriptor is processed. This change improves resource lifecycle management and prevents premature deallocation of network packets, which could otherwise lead to memory corruption or double-free conditions. The mitigation strategy demonstrates proper understanding of kernel networking subsystem behavior and follows established patterns for managing packet descriptors in high-performance network drivers. The solution maintains backward compatibility while strengthening the overall security posture of the wireless driver component within the Linux kernel ecosystem.