High [CVE-2026-9545] Information disclosure via cached SSL session and early data
This high-severity Red Hat Linux advisory covers CVE-2026-9545 affecting Red Hat Hardened Images.
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Summary
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uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate.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. A flaw was found in libcurl.
An attacker can exploit this by replacing a legitimate HTTP/3 server with an impostor machine. This could lead to the disclosure of sensitive information to the attacker.
The version of curl as shipped with Red Hat Enterprise Linux 10 is not built with the support for the ngtcp2 + nghttp3 backend and is therefore unaffected by this issue. Red Hat severity: Moderate — CVSS 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).
Weakness: CWE-295. Affected Red Hat products: Red Hat Hardened Images.
Under investigation: Confidential Compute Attestation; Red Hat Enterprise Linux AI (RHEL AI) 3; Red Hat OpenShift Container Platform 4; Red Hat OpenShift Dev Spaces; Red Hat Trusted Profile Analyzer. Red Hat fixing advisory: RHSA-2026:41240.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 20 days ago·verify at source
- curl-main-8.21.0-0.1.1.hum1
- RHSA-2026:41240
Official advisory · high-confidence parse· fetched 20 days ago·verify at source
Mitigation checklist
- Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Official advisory · high-confidence parse· fetched 20 days ago·verify at source
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