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CVE-2026-53362 is a vulnerability in the Linux kernel’s IPv6 stack that allows an unprivileged local attacker to trigger a heap-based buffer overflow via a UDPv6 socket. The flaw resides in the `__ip6_append_data()` function, specifically in the paged-allocation path used when `MSG_MORE` and `NETIF_F_SG` are set, and a large fragment length is requested. The issue arises from incorrect accounting of the `fraggap` variable—the number of bytes carried over from a previous fragmented packet. In the paged branch, `alloclen` is computed as fragheaderlen + transhdrlen, while `pagedlen` is computed as datalen - transhdrlen, where `datalen` already includes fraggap. When `fraggap` is non-zero (which occurs when this is not the first skb and `transhdrlen` is zero), the linear area of the new skb is undersized by `fraggap` bytes, and `pagedlen` is overstated by the same amount. Consequently, the subsequent copy operation writes past the `skb->end` boundary, corrupting the trailing `skb_shared_info` structure, leading to a heap buffer overflow. This was introduced by commit `773ba4fe9104` (“ipv6: avoid partial copy for zc”) and made triggerable by commit `ce650a166335` (“udp6: Fix __ip6_append_data()’s handling of MSG_SPLICE_PAGES”), which allowed `MSG_SPLICE_PAGES` to proceed in this scenario. The fix involves adding `fraggap` to `alloclen` and subtracting it from pagedlen, ensuring proper sizing and removing the negative copy check exception that was previously used to handle this case.
DailyCVE Form:
Platform: Linux Kernel
Version: 6.0 – 7.1.3
Vulnerability: Heap Buffer Overflow
Severity: Critical
date: August 27, 2026
Prediction: August 30, 2026
What Undercode Say:
Analytics:
Check kernel version uname -r Verify if vulnerable (6.0 <= version < 6.1.177, 6.2-6.6.144, 6.7-6.12.95, 6.13-6.18.38, 6.19-7.1.3) Monitor for unusual UDPv6 traffic with MSG_MORE and MSG_SPLICE_PAGES Log analysis for kernel panics or memory corruption
Exploit: (Educational Purposes!)
Trigger via UDPv6 socket with MSG_MORE and MSG_SPLICE_PAGES Example (conceptual): sendmsg() with MSG_MORE and MSG_SPLICE_PAGES flags Ensure fraggap non-zero by sending fragmented packets This will cause a write past skb->end, corrupting skb_shared_info Compile and run a C program that uses these socket options
Protection:
- Apply kernel patch (commit `e9eacf19281ea2498b36291b56c9606118c2d74e` or later).
- Upgrade to Linux kernel versions 6.1.177, 6.6.144, 6.12.95, 6.18.38, 7.1.3 or higher.
- Disable `MSG_SPLICE_PAGES` if possible (not recommended, breaks functionality).
- Follow CISA BOD 26-04 guidance for patching and mitigation.
Impact:
- Unprivileged local user can trigger a heap buffer overflow.
- Potential for kernel panic, system crash, or arbitrary code execution.
- Affects systems using IPv6 with UDP sockets and specific flags.
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Sources:
Reported By: nvd.nist.gov
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