CVE-2026-99062 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
vsock/virtio: account only unread bytes in read_skb()
After a partial stream receive, rx_bytes tracks the unread suffix while buf_used and peer credit still cover the whole packet. virtio_transport_read_skb() dequeues that packet but passes pkt_len for both counters, underflowing rx_bytes.
On a connected CID_LOCAL stream with an SK_SKB verdict, a 40-byte read from a 100-byte packet made SIOCINQ report -40, an empty recv return ELOOP, and poll report the empty socket readable. After verdict detach, receiving 40 bytes wrapped the counter to zero and hid those queued bytes until one more byte arrived. The fixed run kept the counter balanced and exposed all queued data immediately.
This was found during an LLM-assisted manual source audit of VSOCK receive accounting while re-evaluating virtio_transport_read_skb() after CVE-2024-50169.
Subtract only skb->len minus the VSOCK offset from rx_bytes. Retain the full packet length for buf_used and peer credit.
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Analysis
by VulDB Data Team • 10/23/2026
The Linux kernel vulnerability identified in the virtio vsock subsystem involves a critical accounting error within the read_skb function, specifically affecting how unread bytes are tracked during partial stream receives. This flaw arises from an inconsistency between the rx_bytes counter, which is intended to track only the unread suffix of received data, and other metrics such as buf_used and peer credit that cover the entire packet length. When a partial receive operation occurs, the system dequeues the packet but incorrectly passes the full packet length for both counters rather than adjusting the rx_bytes value to reflect only the remaining unread portion. This miscalculation leads to an underflow of the rx_bytes counter, creating a state where the kernel's internal representation of available data diverges significantly from reality. The issue was discovered during a comprehensive manual source audit assisted by large language models, which re-evaluated the virtio_transport_read_skb function in the context of previous fixes like CVE-2024-50169 to ensure robust receive accounting mechanisms.
The operational impact of this vulnerability is severe for applications relying on connected CID_LOCAL stream sockets with SK_SKB verdicts. When a partial read occurs, such as reading forty bytes from a one hundred byte packet, the underflowed counter causes SIOCINQ to report negative values, indicating an erroneous state where no data appears available despite its presence in the buffer. Subsequent receive operations may return empty results with ELOOP errors, and poll mechanisms incorrectly signal that the socket is readable when it should not be or fail to indicate readiness correctly after a verdict detach. In scenarios involving counter wrapping, queued bytes can remain hidden from applications until additional incoming data forces the counter back into a valid range, leading to significant delays in data processing and potential application hangs or logic errors due to perceived empty buffers.
From a technical classification perspective, this vulnerability aligns with CWE-190 Integer Overflow or Wraparound and CWE-20 Improper Input Validation, as the core issue stems from incorrect arithmetic operations on buffer length counters without proper boundary checks relative to consumed data. In terms of attack vectors, while primarily causing denial-of-service conditions through resource exhaustion or application malfunction rather than direct privilege escalation, it relates to ATT&CK technique T1496 Resource Hijacking by disrupting normal service availability and potentially facilitating further exploitation if an attacker can manipulate the state to cause persistent desynchronization between sender and receiver credits. The fix involves modifying the read_skb logic to subtract only the skb length minus any VSOCK offset from rx_bytes, thereby ensuring that the counter accurately reflects only unread data while retaining full packet lengths for buf_used and peer credit calculations to maintain consistent flow control and buffer management across the virtio transport layer.