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CVE-2026-44621 is a denial-of-service vulnerability affecting applications that embed NLnet Labs libunbound in Unbound up to and including version 1.25.1. When libunbound is configured with a non-zero unwanted-reply-threshold, receipt of enough UDP replies with incorrect transaction IDs can cause the threshold logic to invoke libworker_alloc_cleanup. In affected versions, that function is not present in the libunbound function call allow list. As a result, the cleanup path triggers a fatal exit in libunbound instead of performing the intended cache-flush behavior, which can abruptly terminate the embedding application. The standalone Unbound resolver is not affected because its corresponding cleanup function is registered in the allow list and executes as intended.
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What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
2 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.
No news coverage yet. Advisories and community discussion only.
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.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.