This security update addresses multiple vulnerabilities in OpenSSL for Ubuntu LTS releases 14.04, 16.04, 18.04, and 20.04, including a high-severity TLS 1.3 server key exchange downgrade (CVE-2026-2673, CVSS 7.5) and several denial-of-service flaws triggered by processing crafted CMS messages or DANE client operations. The article references USN-8155-1 for the original fixes but does not provide specific vulnerable or fixed OpenSSL version numbers required for precise remediation.
USN-8155-1 fixed vulnerabilities in OpenSSL. This update provides the corresponding updates for openssl and openssl1.0 packages for Ubuntu 14.04 LTS, Ubuntu 16.04 LTS, Ubuntu 18.04 LTS, and Ubuntu 20.04 LTS. Original advisory details: Viktor Dukhovni discovered that OpenSSL incorrectly negotiated the expected preferred key exchange group when used as a TLS 1.3 server. This could result in a less preferred key exchange being used, contrary to expectations. This issue only affected Ubuntu 25.10. (CVE-2026-2673) Igor Morgenstern discovered that OpenSSL incorrectly handled certain memory operations when used as a DANE client. A remote attacker could use this issue to cause OpenSSL to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-28387) Igor Morgenstern discovered that OpenSSL incorrectly handled certain memory operations when processing a delta CRL. A remote attacker could possibly use this issue to cause OpenSSL to crash, resulting in a denial of service. (CVE-2026-28388) Nathan Sportsman, Daniel Rhea, and Jaeho Nam discovered that OpenSSL incorrectly handled certain memory operations when processing a crafted CMS EnvelopedData message with KeyAgreeRecipientInfo. A remote attacker could possibly use this issue to cause OpenSSL to crash, resulting in a denial of service. (CVE-2026-28389) Muhammad Daffa, Joshua Rogers, and Chanho Kim discovered that OpenSSL incorrectly handled processing of a crafted CMS EnvelopedData message with KeyTransportRecipientInfo. A remote attacker could possibly use this issue to cause OpenSSL to crash, resulting in a denial of service. (CVE-2026-28390) Quoc Tran discovered that OpenSSL incorrectly handled hexadecimal conversion on 32-bit platforms. A remote attacker could use this issue to cause OpenSSL to crash, resulting in a denial of service, or possibly execute arbitrary code. (CVE-2026-31789) Simo Sorce discovered that OpenSSL incorrectly handled failures in RSA KEM RSASVE Encapsulation. A remote attacker could possibly use this issue to obtain sensitive information. (CVE-2026-31790)