CVE-2026-3593Network attack vector

Unauthenticated crash via HTTP/2 SETTINGS frame flood

Published May 20, 2026 · Updated May 20, 2026

Use-after-free in affected BIND 9 releases allows remote attackers to crash named with crafted HTTP/2 traffic sent to a DoH endpoint. While named writes a DoH response, flooding the connection with HTTP/2 SETTINGS frames causes its DoH implementation to access freed heap memory. The unauthenticated network path exists only when DNS-over-HTTPS is enabled; authoritative servers and resolvers are affected.

CVSS severity7.4
High
EPSS probability1.54%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in affected BIND 9 releases allows remote attackers to crash named with crafted HTTP/2 traffic sent to a DoH endpoint. While named writes a DoH response, flooding the connection with HTTP/2 SETTINGS frames causes its DoH implementation to access freed heap memory. The unauthenticated network path exists only when DNS-over-HTTPS is enabled; authoritative servers and resolvers are affected.

The record

CVE
CVE-2026-3593
Published
May 20, 2026
Updated
May 20, 2026
Vendor
Internet Systems Consortium
Product
BIND 9
Classifications
CWE-825, CWE-416, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 20, 2026CVE publishedPublication date reported by the CVE source.
  2. May 20, 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.

  1. Affected versionversion=9.20.0 <=9.20.22
  2. Affected versionversion=9.20.9-S1 <=9.20.22-S1
  3. Affected versionversion=9.21.0 <=9.21.21

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Internet Systems Consortium · BIND 9version=9.20.0 <=9.20.22; version=9.20.9-S1 <=9.20.22-S1; version=9.21.0 <=9.21.21

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.4Red HatCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
7.4Internet Systems Consortium (ISC)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-825Expired Pointer Dereference
CWE-416Use After Free
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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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