Bug 2558739 (CVE-2026-114728)

Summary: CVE-2026-114728 roundcubemail: roundcubemail: Remote content blocking bypass via crafted CSS escape sequences
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Roundcube Webmail. The HTML message sanitizer fails to properly normalize all valid CSS escape sequences when inspecting external resource attributes. A remote attacker can exploit this flaw by sending a crafted email that bypasses remote content blocking, causing external content to load automatically without user consent and resulting in information disclosure.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2562388, 2562389    
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Description OSIDB Bzimport 2026-10-22 02:11:21 UTC 
Roundcube Webmail before 1.6.20 and 1.7.x before 1.7.5 is affected by a remote content blocking bypass in the handling of FuncIRI attributes. rcube_washtml detected the CSS url() token with a pattern that enumerated only some of its escaped spellings, so values using other CSS escape sequences, for example \000075rl( or u\72 l(, were not recognized and remote content was loaded from an HTML message without the user's consent. Upstream fixed this in the commit “Fix remote content blocking bypass via CSS escapes in FuncIRI attributes (again)”, which resolves CSS escapes before matching and also inspects the `to`, `from` and `by` attributes.