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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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
Which versions are affected by CVE-2026-10657?
It affects 1 product.
Products include 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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-10657 being exploited?
There is no known exploitation of CVE-2026-10657 in the wild and no public exploit code.
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Sources
Also known as GHSA-76jh-3j5f-9vq4.