CVE-2026-98549
Received Received - Intake

TCP Collapse Fence Bypass in Linux Kernel

Publication date: 2026-10-18

Last updated on: 2026-10-18

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: tcp: prevent collapsing skbs across boundary in rtx queue tcp_write_collapse_fence() sets TCP_SKB_CB(skb)->eor = 1 on tcp_write_queue_tail(sk) to prevent skbs queued after a switch to device encryption from being collapsed into earlier skbs. The fence is a no-op if all earlier data has already been transmitted when the switch happens: sk->sk_write_queue is empty. The not yet acknowledged earlier skbs wait in sk->tcp_rtx_queue with eor 0. On a subsequent retransmit or SACK shift, tcp_retrans_try_collapse() or tcp_shift_skb_data() can then merge an skb queued after the switch into one queued before it. Both users of the fence are affected: - psp: devices only encrypt skbs with skb->decrypted set. The merged skb keeps decrypted = 0 from the earlier skb, so merged data sent after psp_sock_assoc_set_tx() is retransmitted in cleartext. - tls device offload: the merged skb straddles the start marker set in tls_set_device_offload(). The software fallback (fill_sg_in() returns -EINVAL) and the mlx5, nfp and funeth drivers cannot handle such an skb and drop it. Every retransmit rebuilds the same skb, so the connection stalls. Fix this in two places, for defense in depth: 1. Fall back to tcp_rtx_queue_tail(sk) in tcp_write_collapse_fence() when tcp_write_queue_tail(sk) is NULL. 2. Check !skb_cmp_decrypted(to, from) in tcp_skb_can_collapse(), as tcp_skb_can_collapse_rx() does on receive. skb_shift(), which both collapse paths call, already has a DEBUG_NET_WARN_ON_ONCE() for this condition.

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Meta Information

Published
2026-10-18
Last Modified
2026-10-18
Generated
2026-10-18
AI Q&A
2026-10-18
EPSS Evaluated
N/A
NVD
CVE-2026-98549
EUVD
EUVD-2026-103594

Affected Vendors & Products

Showing 5 associated CPEs
Vendor Product Version / Range
Linux Linux e8f69799810c32dd40c6724d829eccc70baad07f
Linux Linux e8f69799810c32dd40c6724d829eccc70baad07f
Linux Linux e8f69799810c32dd40c6724d829eccc70baad07f
Linux Linux e8f69799810c32dd40c6724d829eccc70baad07f
Linux Linux 4.18

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability in the Linux kernel involves improper handling of TCP retransmission queues when switching to device encryption. It allows encrypted and unencrypted data segments to be merged incorrectly, potentially exposing sensitive data or causing connection failures.

Detection Guidance

This vulnerability affects the Linux kernel's TCP retransmission queue handling, specifically related to encryption boundaries. Detection requires checking kernel logs for retransmission errors or connection stalls, particularly with PSP or TLS offload devices. Monitor for 'skb_shift' errors or mlx5/nfp/funeth driver failures in system logs.

Impact Analysis

If exploited, this flaw could lead to data leaks where encrypted data is retransmitted in plaintext or cause network connections to stall due to malformed packets. Systems using PSP encryption or TLS device offloading are particularly affected.

Compliance Impact

This vulnerability could violate compliance requirements by exposing sensitive data in transit, potentially breaching GDPR's data protection principles or HIPAA's encryption mandates for protected health information.

Mitigation Strategies

Apply the Linux kernel patch addressing tcp_write_collapse_fence() and tcp_skb_can_collapse() issues. Update to a patched kernel version. If using PSP or TLS offload, verify device driver compatibility with retransmission handling. Monitor for retransmission errors post-update.

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