Bug 2503062 (CVE-2026-40691)
| Summary: | CVE-2026-40691 unbound: Unbound: Denial of Service via crafted DNSCrypt query | ||
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| Product: | [Other] Security Response | Reporter: | OSIDB Bzimport <bzimport> |
| Component: | vulnerability-draft | Assignee: | Product Security <prodsec-ir-bot> |
| Status: | NEW --- | QA Contact: | |
| Severity: | high | Docs Contact: | |
| Priority: | high | ||
| Version: | unspecified | CC: | akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, security-response-team, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers |
| Target Milestone: | --- | Keywords: | Security |
| Target Release: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | --- | |
| Doc Text: |
A flaw was found in Unbound, a domain name system (DNS) resolver. When Unbound is configured with DNSCrypt support, a remote attacker could send a specially crafted DNSCrypt query over TCP. This malicious query could cause a memory error, leading to a server crash and a Denial of Service (DoS). This means legitimate users would be unable to access services relying on the Unbound server.
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Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | Type: | --- | |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
| Bug Depends On: | 2506178 | ||
| Bug Blocks: | |||
| Deadline: | 2026-07-22 | ||
A denial of service vulnerability has been discovered in Unbound when compiled with DNSCrypt support ('--enable-dnscrypt'). A single bad DNSCrypt query over TCP could underflow Unbound's DNSCrypt packet reading procedure that may lead to heap overflow and eventual server crash and denial of service. Unbound 1.25.2 includes fixes to select the proper buffer TCP buffer for DNSCrypt, to properly check against the buffer's capacity and to clear the buffer before writing the dnscrypt contents otherwise UDP queries can hit assertions.