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CVE-2026-3593 is a heap use-after-free vulnerability in ISC BIND 9’s DNS-over-HTTPS (DoH) implementation, specifically in the HTTP/2 handling path in lib/isc/netmgr/http.c. The flaw is caused by a dangling pointer condition where socket->h2->wbuf can continue to reference freed DoH response memory after the response/request structure is released. The vulnerable path involves server_read_callback, which can subsequently read from the stale buffer via memmove(). The issue can be triggered by crafted HTTP/2 traffic, particularly repeated SETTINGS frames that modify INITIAL_WINDOW_SIZE, causing nghttp2 to re-evaluate flow control and re-invoke the callback after the response buffer has already been freed. This results in memory corruption and a confirmed heap use-after-free read. Affected versions are BIND 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9.18.x and 9.18.x-S1 are explicitly not affected.
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No public exploit code observed for this vulnerability.
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17 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A use-after-free vulnerability in ISC BIND 9 DNS-over-HTTPS handling that can trigger denial of service on hardened/ASAN builds when HTTP/2 SETTINGS frames cause nghttp2 to re-read a freed response buffer.
A heap use-after-free vulnerability in ISC BIND 9 DNS-over-HTTPS (DoH) implementation that can cause memory corruption, crashes, and potentially arbitrary code execution.
A use-after-free memory corruption vulnerability in BIND 9 DNS-over-HTTPS handling that can be triggered by malicious HTTP/2 traffic against secure endpoints.
A heap use-after-free vulnerability in the BIND 9 DNS-over-HTTPS implementation.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
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Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.