CVE-2026-82717: CNAME synthesis could lead to heap corruption
In NLnet Labs Unbound up to and including 1.26.0, a vulnerability was found in that can progressively corrupt heap memory and under certain systems and compilation options could lead to remote code execution. The vulnerability starts when CNAME synthesis during an upstream response needs to enforce(rewrite) a max TTL value in the packet buffer. Coupled with a compression pointer that points to the overwritten value and invalidates the domain name, it leads to an error path that does not properly move the buffer position and allows for the heap buffer overflow. Since this is heavily reliant on heap memory layout, results are memory corruption that eventually leads to a crash and under specific systems and compilation options remote code execution.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
NLnet Labs Unboundto a version that resolves this vulnerability.Fixed in 1.26.1
Event History
Frequently Asked Questions
What conditions are needed to reach the vulnerable code path?
An upstream response must trigger CNAME synthesis that rewrites a maximum TTL value in the packet buffer. A compression pointer must also reference the overwritten value in a way that invalidates the domain name, causing an error path to mishandle the buffer position.
Is remote code execution expected in every successful attack?
No. The reported result is progressive heap corruption that can lead to a crash. Remote code execution is possible only under certain system and compilation options and depends heavily on the heap memory layout.