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CVE-2026-82717— CNAME synthesis could lead to heap corruption

Quick assessment

Affected
NLnet Labs Unbound
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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 durin

CVSS 8.4 · High
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I. Basic Information for CVE-2026-82717

Vulnerability Information
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Vulnerability Title
CNAME synthesis could lead to heap corruption
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:U
Source: CVE Program / CVE List V5
Vulnerability Type
堆缓冲区溢出
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
NLnet Labs Unbound 0 ~ 1.26.1 -

II. Public POCs for CVE-2026-82717

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III. Intelligence Information for CVE-2026-82717

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Other References for CVE-2026-82717 (1)

Same Patch Batch · NLnet Labs · 2026-09-16 · 9 CVEs total

CVE-2026-81642 9.1 CRITICAL Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY
CVE-2026-81634 7.5 HIGH Possible heap buffer overflow during DNSSEC canonicalization
CVE-2026-78227 6.5 MEDIUM Use-after-free in DoQ stream output buffer on reset re-transmission
CVE-2026-82720 5.9 MEDIUM Use-after-free in DoH stream cleanup code path
CVE-2026-85501 5.3 MEDIUM Retrap: Novel Vulnerabilities to launch Algorithmic Complexity Attacks on DNSSEC
CVE-2026-80225 5.3 MEDIUM Possible degradation of service from continuous queries on the same TCP/DoT connection
CVE-2026-77955 4.4 MEDIUM Possible ZONEMD verification bypass window
CVE-2026-77860 3.7 LOW 'serve-expired' can bypass Unbound 'wait-limit'

IV. Related Vulnerabilities

Same product: Unbound
Same vendor: NLnet Labs
Same weakness: CWE-122

V. Comments for CVE-2026-82717

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