{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-40691", "assignerOrgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6", "state": "PUBLISHED", "assignerShortName": "NLnet Labs", "dateReserved": "2026-06-22T10:11:10.532Z", "datePublished": "2026-07-22T13:04:35.410Z", "dateUpdated": "2026-07-22T14:31:26.565Z"}, "containers": {"cna": {"title": "Packet of death for DNSCrypt over TCP", "datePublic": "2026-07-22T00:00:00.000Z", "affected": [{"vendor": "NLnet Labs", "product": "Unbound", "versions": [{"version": "1.9.0", "status": "affected", "lessThan": "1.25.2", "versionType": "semver"}], "defaultStatus": "unaffected"}], "descriptions": [{"lang": "en", "value": "In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to 'msg-buffer-size', writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support ('--enable-dnscrypt') and the 'dnscrypt:' clause to be configured and enabled for the listening interfaces."}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "Unbound compiled with DNSCrypt ('--enable-dnscrypt')"}], "cvssV3_1": {"version": "3.1", "baseScore": 7.5, "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}}], "problemTypes": [{"descriptions": [{"lang": "en", "cweId": "CWE-122", "description": "CWE-122: Heap-based Buffer Overflow", "type": "CWE"}, {"lang": "en", "cweId": "CWE-787", "description": "CWE-787: Out-of-bounds Write", "type": "CWE"}]}], "solutions": [{"lang": "en", "value": "This issue is fixed starting with version 1.25.2"}], "timeline": [{"time": "2026-05-18T00:00:00.000Z", "lang": "en", "value": "Issue reported by Qifan Zhang"}, {"time": "2026-06-10T00:00:00.000Z", "lang": "en", "value": "NLnet Labs shares patch with Qifan Zhang"}, {"time": "2026-06-13T00:00:00.000Z", "lang": "en", "value": "Qifan Zhang verifies patch"}, {"time": "2026-06-30T00:00:00.000Z", "lang": "en", "value": "Issue reported by Trung Nguyen"}, {"time": "2026-07-02T00:00:00.000Z", "lang": "en", "value": "NLnet Labs shares patch with Trung Nguyen"}, {"time": "2026-07-02T00:00:00.000Z", "lang": "en", "value": "Trung Nguyen suggests extra fixes"}, {"time": "2026-07-03T00:00:00.000Z", "lang": "en", "value": "NLnet Labs shares new version of the patch with Trung Nguyen"}, {"time": "2026-07-04T00:00:00.000Z", "lang": "en", "value": "Trung Nguyen verifies patch"}, {"time": "2026-07-22T00:00:00.000Z", "lang": "en", "value": "Fixes released with version 1.25.2"}], "credits": [{"lang": "en", "value": "Qifan Zhang (Palo Alto Networks)", "type": "finder"}, {"lang": "en", "value": "Trung Nguyen (@everping, CyStack)", "type": "finder"}], "references": [{"url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40691.txt", "tags": ["vendor-advisory"]}], "providerMetadata": {"orgId": "206fc3a0-e175-490b-9eaa-a5738056c9f6", "shortName": "NLnet Labs", "dateUpdated": "2026-07-22T13:04:35.410Z"}, "x_generator": {"engine": "cvelib 1.8.0"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-07-22T14:30:33.327603Z", "id": "CVE-2026-40691", "options": [{"Exploitation": "none"}, {"Automatable": "yes"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-07-22T14:31:26.565Z"}}]}}

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