# CVE-2026-10657: Out-of-bounds read in Zephyr DNS resolver mDNS suffix check (memcmp past string NUL)

> An out-of-bounds read in Zephyr's DNS resolver can cause a denial of service when processing short hostname suffixes if mDNS support is enabled.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Jul 2026
- **Updated:** 15 Oct 2026
- **Also known as:** GHSA-76jh-3j5f-9vq4

## What is CVE-2026-10657?

CVE-2026-10657 is a low-severity denial of service vulnerability in Zephyrproject Zephyr, published on 5 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Zephyr's DNS resolver detects mDNS (.local) queries in dns_resolve_name_internal() (subsys/net/lib/dns/resolve.c) with memcmp(strrchr(query, '.'), ".local", 7), which always reads a fixed 7 bytes from the suffix pointer. When the resolved hostname's final label is shorter than 7 bytes (e.g. names ending in .org, .com, .net, .io, or a trailing dot), the comparison reads 1-2 bytes past the string's NUL terminator.

The hostname (query) is the caller-supplied name passed through the standard getaddrinfo()/dns_get_addr_info()/dns_resolve_name() path and is influenceable by operators or remote inputs (server names from configuration, parsed URLs, or app-facing interfaces).

On a tightly-sized buffer with no slack (for example a userspace getaddrinfo call where the hostname is copied with k_usermode_string_alloc_copy to exactly strlen+1 bytes), the over-read crosses the allocation boundary; if that boundary is unmapped (guard page, memory-domain boundary under MPU, or an address sanitizer) the over-read faults, causing a denial of service. The over-read bytes are never returned, so there is no information disclosure.

The flaw is compiled only when CONFIG_MDNS_RESOLVER is enabled, exists since v1.10.0, and is fixed by replacing the fixed-length memcmp with a NUL-safe strcmp(ptr, ".local").

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-10657?

It affects 1 product.


Products: Zephyrproject Zephyr.

## How do I fix CVE-2026-10657?

No fix has been published for CVE-2026-10657 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-10657 being exploited?

There is no known exploitation of CVE-2026-10657 in the wild and no public exploit code.

## Other vulnerabilities in Zephyrproject Zephyr

- [CVE-2026-5067](https://insights.sbomify.com/CVE-2026-5067/): Out-of-bounds read/write in HTTP WebSocket upgrade via non-null-terminated Sec-WebSocket-Key (critical 9.8)
- [CVE-2022-3806](https://insights.sbomify.com/CVE-2022-3806/): Bluetooth HCI Error Handling Double Free (critical 9.8)
- [CVE-2017-14199](https://insights.sbomify.com/CVE-2017-14199/): Memory corruption in getaddrinfo (critical 9.8)
- [CVE-2018-1000800](https://insights.sbomify.com/CVE-2018-1000800/): Null dereference in n/a (critical 9.8)
- [CVE-2021-3329](https://insights.sbomify.com/CVE-2021-3329/): DOS: Incorrect handling of the initial HCI ACL_MTU handshake packet leads to crash of bluetooth host layer (critical 9.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-10657 and fix it if it is affected.

What it is: CVE-2026-10657 is a low-severity denial of service vulnerability in Zephyrproject Zephyr, published on 5 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-10657 in the wild and no public exploit code.

Affected product: Zephyrproject Zephyr. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-10657/ (Markdown: https://insights.sbomify.com/CVE-2026-10657/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-10657
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-10657
- OSV: https://osv.dev/vulnerability/CVE-2026-10657

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-10657/
Summaries are generated and may contain mistakes; the official description above is the record.