Remote code execution via miscounted DoQ buffer
Published Jul 25, 2026 · Updated Jul 25, 2026
Heap buffer overflow in the DoQ listener in CZ.NIC Knot Resolver before 6.4.1 allows remote attackers to execute code via QUIC frames. kr_recv_stream_data_cb() accumulates each frame length into pers_inbuf.size instead of resetting it to the allocation's new total, so a later memcpy skips reallocation and writes beyond the heap object. An unauthenticated attacker must reach an enabled DoQ port; successful grooming executes code as the service user, while failed attempts crash a worker.
Summary
What happened
Heap buffer overflow in the DoQ listener in CZ.NIC Knot Resolver before 6.4.1 allows remote attackers to execute code via QUIC frames. kr_recv_stream_data_cb() accumulates each frame length into pers_inbuf.size instead of resetting it to the allocation's new total, so a later memcpy skips reallocation and writes beyond the heap object. An unauthenticated attacker must reach an enabled DoQ port; successful grooming executes code as the service user, while failed attempts crash a worker.
The record
- CVE
- CVE-2026-66374
- Published
- Jul 25, 2026
- Updated
- Jul 25, 2026
- Vendor
- CZ.NIC
- Product
- Knot Resolver
- Classifications
- CWE-1284, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 25, 2026CVE publishedPublication date reported by the CVE source.
- Jul 25, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <6.4.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- knot-doq proof of conceptfunctional · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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