# CVE-2026-42768: Multi-RecipientInfo Bleichenbacher Oracle in CMS_decrypt() and PKCS7_decrypt() CVE-2026-42768 is fixed in 14 products on 1 platform, first by libssl3t64 3.5.5-1ubuntu3.2, released June 8, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-42768 - Priority: High - CVSS: 9.1 (Low) - EPSS: 0.0080 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jun 8, 2026 - Weakness: Covert Channel - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42768 ## Description Issue summary: The CMS_decrypt and PKCS7_decrypt functions are vulnerable to Bleichenbacher-style attack when an attacker is able to provide the CMS or S/MIME messages and observe the error code and/or decryption output. Impact summary: The Bleichenbacher-style attack allows an attacker to use the victim's vulnerable application as a way to decrypt or sign messages with the victim's private RSA key. The attack is possible in 2 variants. 1. The decryption API (CMS_decrypt(), PKCS7_decrypt()) is used without providing the recipient certificate. In this case OpenSSL iterates over every KeyTransRecipientInfo (KTRI) without stopping at the first success. An attacker who authors a message with two KTRI entries — the first one wrapping a real CEK under the victim's public key, the second with an arbitrary probe ciphertext — obtains opportunity to iterate the 2nd KTRI to get a valid PKCS#1 v1.5 padding if the error code of the application is available. That is a Bleichenbacher oracle (Bleichenbacher, CRYPTO '98): an adaptive-chosen-ciphertext side channel from which the attacker decrypts any RSA ciphertext to the victim's key or forges any PKCS#1 v1.5 signature under it. 2. When the decryption API (CMS_decrypt(), PKCS7_decrypt()) is provided with the recipient certificate, and the recipient is not found, a random key is substituted. An attacker who authors a message and is able to compare both error code and the result of the decryption, can mount a Bleichenbacher oracle. We are not aware of any applications that provide a remote attacker an opportunity to mount an attack described in these scenarios. We consider the existence of such application very unlikely, and for this reason this CVE has been evaluated as Low severity. To avoid these attacks, when RSA PKCS#1 v1.5 Key Transport is in use, the invoked EVP_PKEY_decrypt() will use the implicit rejection mechanism described in draft-irtf-cfrg-rsa-guidance. In previous OpenSSL releases the implicit rejection was explicitly disabled. The implicit rejection mechanism always returns a plaintext value, the symmetric key. This result is deterministic for the ciphertext and the private key. The length of the decryption result can happen to match the length of the key of the symmetric cipher that was used for the content encryption. When a certificate is not provided, the last RecipientInfo producing a key that looks valid will be used. It may cause getting garbage content on decryption. As a proper way to deal with this a recipient certificate has to be provided to identify the particular RecipientInfo for decryption. The FIPS modules in 4.0, 3.6, 3.5, and 3.4 are not affected by this issue, as CMS and S/MIME processing happens outside the OpenSSL FIPS module boundary. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | libssl3t64 Ubuntu 25.10 (questing) | 3.5.3-1ubuntu3.4 | [libssl3t64 3.5.3-1ubuntu3.4](https://patchblox.com/security/data/fix/linux/ubuntu-questing-libssl3t64-3.5.3-1ubuntu3.4.md) | Jun 24, 2026 | | Linux | libssl3t64 Ubuntu 26.04.1 LTS (resolute) | 3.5.5-1ubuntu3.2 | [libssl3t64 3.5.5-1ubuntu3.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libssl3t64-3.5.5-1ubuntu3.2.md) | Jun 8, 2026 | | Linux | openssl Debian 13.5 (trixie) | 3.5.6-1~deb13u2 | [DEBIAN-CVE-2026-42768](https://patchblox.com/security/data/fix/linux/debian-cve-2026-42768.md) | Jun 24, 2026 | | Linux | openssl Debian 14 | 3.6.3-1 | [DEBIAN-CVE-2026-42768](https://patchblox.com/security/data/fix/linux/debian-cve-2026-42768.md) | Jun 24, 2026 | | Linux | openssl RHEL 10 | 3.5.5-4.el10_2 | [RHSA-2026:25237](https://patchblox.com/security/data/fix/linux/rhsa-2026-25237.md) | Jun 24, 2026 | | Linux | openssl RHEL 9 | 1:3.5.5-4.el9_8 | [RHSA-2026:25239](https://patchblox.com/security/data/fix/linux/rhsa-2026-25239.md) | Jun 24, 2026 | | Linux | openssl Ubuntu 25.10 (questing) | 3.5.3-1ubuntu3.4 | [openssl 3.5.3-1ubuntu3.4](https://patchblox.com/security/data/fix/linux/ubuntu-questing-openssl-3.5.3-1ubuntu3.4.md) | Jun 24, 2026 | | Linux | openssl Ubuntu 26.04.1 LTS (resolute) | 3.5.5-1ubuntu3.2 | [openssl 3.5.5-1ubuntu3.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-openssl-3.5.5-1ubuntu3.2.md) | Jun 8, 2026 | | Linux | openssl almalinux 10 | 1:3.5.5-4.el10_2.alma.1 | [ALSA-2026:25237](https://patchblox.com/security/data/fix/linux/alsa-2026-25237.md) | Jun 11, 2026 | | Linux | openssl almalinux 9 | 1:3.5.5-4.el9_8 | [ALSA-2026:25239](https://patchblox.com/security/data/fix/linux/alsa-2026-25239.md) | Jun 11, 2026 | | Linux | openssl amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl ol 10 | 1:3.5.5-5.0.1.el10_2 | [ELSA-2026-25237](https://patchblox.com/security/data/fix/linux/elsa-2026-25237.md) | Jul 28, 2026 | | Linux | openssl ol 9 | 1:3.5.5-4.0.1.el9_8 | [ELSA-2026-25239](https://patchblox.com/security/data/fix/linux/elsa-2026-25239.md) | Jun 23, 2026 | | Linux | openssl rocky 10 | 1:3.5.5-4.el10_2 | [RLSA-2026:25237](https://patchblox.com/security/data/fix/linux/rlsa-2026-25237.md) | Jun 13, 2026 | | Linux | openssl rocky 9 | 1:3.5.5-4.el9_8 | [RLSA-2026:25239](https://patchblox.com/security/data/fix/linux/rlsa-2026-25239.md) | Jun 13, 2026 | | Linux | openssl-3 opensuse-leap 16.0 | 3.5.0-160000.8.1 | [OPENSUSE-SU-2026:21005-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21005-1.md) | Jun 22, 2026 | | Linux | openssl-3 sles 15.7 | 3.2.3-150700.5.36.1 | [SUSE-SU-2026:2648-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-2648-1.md) | Jun 26, 2026 | | Linux | openssl-3 sles 16.0 | 3.5.0-160000.8.1 | [SUSE-SU-2026:22315-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-22315-1.md) | Jun 22, 2026 | | Linux | openssl-debuginfo amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-debugsource amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-devel RHEL 9 | 1:3.5.5-4.el9_8 | [RHSA-2026:25239](https://patchblox.com/security/data/fix/linux/rhsa-2026-25239.md) | Jun 24, 2026 | | Linux | openssl-devel almalinux 10 | 1:3.5.5-4.el10_2.alma.1 | [ALSA-2026:25237](https://patchblox.com/security/data/fix/linux/alsa-2026-25237.md) | Jun 11, 2026 | | Linux | openssl-devel almalinux 9 | 1:3.5.5-4.el9_8 | [ALSA-2026:25239](https://patchblox.com/security/data/fix/linux/alsa-2026-25239.md) | Jun 11, 2026 | | Linux | openssl-devel amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-devel ol 10 | 1:3.5.5-5.0.1.el10_2 | [ELSA-2026-25237](https://patchblox.com/security/data/fix/linux/elsa-2026-25237.md) | Jul 28, 2026 | | Linux | openssl-devel ol 9 | 1:3.5.5-4.0.1.el9_8 | [ELSA-2026-25239](https://patchblox.com/security/data/fix/linux/elsa-2026-25239.md) | Jun 23, 2026 | | Linux | openssl-fips-provider-latest amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-fips-provider-latest-debuginfo amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-libs RHEL 9 | 1:3.5.5-4.el9_8 | [RHSA-2026:25239](https://patchblox.com/security/data/fix/linux/rhsa-2026-25239.md) | Jun 24, 2026 | | Linux | openssl-libs almalinux 10 | 1:3.5.5-4.el10_2.alma.1 | [ALSA-2026:25237](https://patchblox.com/security/data/fix/linux/alsa-2026-25237.md) | Jun 11, 2026 | | Linux | openssl-libs almalinux 9 | 1:3.5.5-4.el9_8 | [ALSA-2026:25239](https://patchblox.com/security/data/fix/linux/alsa-2026-25239.md) | Jun 11, 2026 | | Linux | openssl-libs amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-libs ol 10 | 1:3.5.5-5.0.1.el10_2 | [ELSA-2026-25237](https://patchblox.com/security/data/fix/linux/elsa-2026-25237.md) | Jul 28, 2026 | | Linux | openssl-libs ol 9 | 1:3.5.5-4.0.1.el9_8 | [ELSA-2026-25239](https://patchblox.com/security/data/fix/linux/elsa-2026-25239.md) | Jun 23, 2026 | | Linux | openssl-libs-debuginfo amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-perl RHEL 9 | 1:3.5.5-4.el9_8 | [RHSA-2026:25239](https://patchblox.com/security/data/fix/linux/rhsa-2026-25239.md) | Jun 24, 2026 | | Linux | openssl-perl almalinux 10 | 1:3.5.5-4.el10_2.alma.1 | [ALSA-2026:25237](https://patchblox.com/security/data/fix/linux/alsa-2026-25237.md) | Jun 11, 2026 | | Linux | openssl-perl almalinux 9 | 1:3.5.5-4.el9_8 | [ALSA-2026:25239](https://patchblox.com/security/data/fix/linux/alsa-2026-25239.md) | Jun 11, 2026 | | Linux | openssl-perl amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-perl ol 10 | 1:3.5.5-5.0.1.el10_2 | [ELSA-2026-25237](https://patchblox.com/security/data/fix/linux/elsa-2026-25237.md) | Jul 28, 2026 | | Linux | openssl-perl ol 9 | 1:3.5.5-4.0.1.el9_8 | [ELSA-2026-25239](https://patchblox.com/security/data/fix/linux/elsa-2026-25239.md) | Jun 23, 2026 | | Linux | openssl-provider-legacy Ubuntu 25.10 (questing) | 3.5.3-1ubuntu3.4 | [openssl-provider-legacy 3.5.3-1ubuntu3.4](https://patchblox.com/security/data/fix/linux/ubuntu-questing-openssl-provider-legacy-3.5.3-1ubuntu3.4.md) | Jun 24, 2026 | | Linux | openssl-provider-legacy Ubuntu 26.04.1 LTS (resolute) | 3.5.5-1ubuntu3.2 | [openssl-provider-legacy 3.5.5-1ubuntu3.2](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-openssl-provider-legacy-3.5.5-1ubuntu3.2.md) | Jun 8, 2026 | | Linux | openssl-snapsafe-libs amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | | Linux | openssl-snapsafe-libs-debuginfo amzn 2023 | 1:3.5.5-1.amzn2023.0.5 | [ALAS2023-2026-1853](https://patchblox.com/security/data/fix/linux/alas2023-2026-1853.md) | Jun 22, 2026 | --- Data as of 2026-11-08T19:12:23Z UTC. 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