Bug 2520645 (CVE-2026-73253)

Summary: CVE-2026-73253 mongoose: Mongoose: TLS Hostname Verification Bypass via Overly Permissive Wildcard Matching
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: urgent    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Mongoose. Wildcard certificate matching in its built-in Transport Layer Security (TLS) stack does not properly restrict matches to a single domain level. An on-path network attacker with a valid wildcard certificate for a parent domain could exploit this flaw to bypass hostname verification and impersonate subdomains. Successful exploitation allows an attacker to intercept and modify sensitive encrypted network traffic.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2538668    
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Description OSIDB Bzimport 2026-08-20 17:56:09 UTC 
Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c call mg_match(), whose wildcard can cross DNS label boundaries, so a pattern such as *.example.com can match foo.bar.example.com. The resulting hostname verification bypass permits interception and modification of TLS traffic. This issue is fixed in version 7.22.