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.
CVE-2026-40691
HIGHPre-NVD 7.57.5—Trending — 4 sources updated this week
EchelonGraph scoreHIGH confidence
Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-07-22. a secondary CVSS source baseline 7.5; sources differ by 0.0.
Triggered by: GitHub Security Advisory CVSS
Sources: ghsa, secondary
7.5
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 7.5Exploit: NoneExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 7.5
- EG Score
- 7.5(high)
- EG Risk
- 49(Track)EG Risk 49/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity75% × 45%Exploitation0% × 40%Automatability100% × 15%Action: Routine — remediate on your standard cadence. - EPSS
- 22.7%
- KEV
- Not listed
Published
July 22, 2026
Last Modified
July 24, 2026
Advisory Details (1)
Auto-updated Jul 22, 2026No patch confirmed yet.
Vendor Advisories for CVE-2026-40691(3)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- CVE-2026-40691Microsoft Security Response Center (MSRC)Medium
Packet of death for DNSCrypt over TCP
- GHSA-vxvj-6rhp-3pqqGitHub Security AdvisoriesHigh
In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the...
- RHSA-2026:43588Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update
Weakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 11× in last 7d / 11× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-25 14:18 UTCEPSS rescore
- 2026-07-24 14:17 UTCEPSS rescore
- 2026-07-23 14:18 UTCEPSS rescore
- 2026-07-23 14:18 UTCEPSS rescore
- 2026-07-23 03:11 UTCEG score recompute
- 2026-07-22 22:04 UTCEG score recompute
- 2026-07-22 22:04 UTCGHSA enrichment
- 2026-07-22 15:34 UTCEG score recompute
- 2026-07-22 15:34 UTCGHSA enrichment
- 2026-07-22 13:19 UTCEG score recompute
- 2026-07-22 13:17 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Same CWE
10 shownCWE-122 · CWE-787
- CVE-2006-10003EG 9.8CRITICAL
- CVE-2007-0158EG 9.8CRITICAL
- CVE-2007-0899EG 9.8CRITICAL
- CVE-2011-2462EG 9.8 KEVEPSS 100%CRITICAL
- CVE-2010-20115EG 9.3CRITICAL
- CVE-2010-4398NVD 7.8EG 9.0 KEVEPSS 95%HIGH
- CVE-2010-3333NVD 7.8EG 9.0 KEVEPSS 100%HIGH
- CVE-2010-2883NVD 7.3EG 9.0 KEVEPSS 100%HIGH
- CVE-2010-1297NVD 7.8EG 9.0 KEVEPSS 100%HIGH
- CVE-2009-3953NVD 8.8EG 9.0 KEVEPSS 100%HIGH
Frequently asked(5)
What is CVE-2026-40691?
CVE-2026-40691 is a high vulnerability published on July 22, 2026. 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…
When was CVE-2026-40691 disclosed?
CVE-2026-40691 was first published in the National Vulnerability Database on July 22, 2026, with the most recent update on July 24, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-40691 actively exploited?
CVE-2026-40691 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 22.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-40691?
CVE-2026-40691 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-40691?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-40691, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-40691
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