Bug 2496756 (CVE-2026-9545)

Summary:	CVE-2026-9545 libcurl: libcurl: Information disclosure via cached SSL session and early data
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	bbrownin, csutherl, dbosanac, gtanzill, jbuscemi, jclere, jmitchel, jreimann, kshier, mdessi, mrizzi, pcattana, pjindal, plodge, rekumar, rhel-process-autobot, sdawley, stcannon, szappis, teagle, vchlup, vvoronko, watson-tool-maintainers, yguenane
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in libcurl. An attacker can exploit this by replacing a legitimate HTTP/3 server with an impostor machine. When libcurl attempts a second transfer to the same site with a cached SSL session and early data enabled, it may send sensitive request data before verifying the server's certificate. This could lead to the disclosure of sensitive information to the attacker.	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:	2509784, 2497440
Bug Blocks:

Description OSIDB Bzimport 2026-07-03 07:01:29 UTC

In this scenario, libcurl first uses a proper HTTP/3 server for the initial
transfers, and when it makes a second transfer to the same site it has been
replaced by the attacker's impostor machine - without a valid certificate.

When libcurl returns to the hostname the second time with a cached SSL session
(`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the
`CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might
send off the second request's bytes on that new connection *before* enforcing
the certificate verification failure. Potentially leaking sensitive
information.

Comment 4 errata-xmlrpc 2026-08-19 13:28:43 UTC

This issue has been addressed in the following products:

  Red Hat JBoss Core Services 2.4.62.SP5

Via RHSA-2026:56869 https://access.redhat.com/errata/RHSA-2026:56869