Skip to content
Fencer Vulns
low 3.7

CVE-2026-42768 json

Multi-RecipientInfo Bleichenbacher Oracle in CMS_decrypt() and PKCS7_decrypt()

published 2026-06-09 5 mo ago modified 2026-08-13 2 mo ago also EUVD-2026-35485 , GHSA-5m8f-m8jv-3rp3 , JLSEC-2026-1140

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 56%
public exploits
0
none known

Summary

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.

Patch / fix

  • julia AppBundler 1.0.1
  • julia OpenSSL_jll 3.5.7+0
  • OpenSSL OpenSSL 3.4.6, 3.5.7, 3.6.3, 4.0.1
  • openssl Debian 13 3.5.6-1~deb13u2
  • openssl Debian 14 3.6.3-1

debian advisories DEBIAN-CVE-2026-42768

  • openssl Ubuntu 25.10 3.5.3-1ubuntu3.4
  • openssl Ubuntu 26.04 LTS 3.5.5-1ubuntu3.2

ubuntu advisories UBUNTU-CVE-2026-42768

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • bootupd hummingbird 1 0.3.2-1.hum1
  • rust-bootupd hummingbird 1 0.3.2-1.hum1
  • ruby3.4 hummingbird 1 3.4.10-31.7.hum1
  • ruby3.4-libs hummingbird 1 3.4.10-31.7.hum1
  • ruby3.4-bundled-gems hummingbird 1 3.4.10-31.7.hum1
  • ruby3.4-default-gems hummingbird 1 3.4.10-31.7.hum1
  • ruby4.0 hummingbird 1 4.0.6-37.3.hum1
  • ruby4.0-libs hummingbird 1 4.0.6-37.3.hum1

red hat advisories RHSA-2026:67551RHSA-2026:62790RHSA-2026:62563RHSA-2026:62562RHSA-2026:55543RHSA-2026:42825

  • openssl-3 SLE Module for Basesystem 15 SP7 3.2.3-150700.5.36.1
  • openssl-3 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 3.5.0-160000.8.1

suse advisories SUSE-SU-2026:2648-1SUSE-SU-2026:22251-1SUSE-SU-2026:22315-1

  • openssl-3 openSUSE Leap 16.0 3.5.0-160000.8.1
  • openssl-3 openSUSE Tumbleweed 3.5.3-6.1

opensuse advisories openSUSE-SU-2026:21005-1openSUSE-SU-2026:11023-1

  • openssl AlmaLinux 10 1:3.5.5-4.el10_2.alma.1
  • openssl-libs AlmaLinux 10 1:3.5.5-4.el10_2.alma.1
  • openssl-perl AlmaLinux 10 1:3.5.5-4.el10_2.alma.1
  • openssl AlmaLinux 9 1:3.5.5-4.el9_8
  • openssl-libs AlmaLinux 9 1:3.5.5-4.el9_8
  • openssl-perl AlmaLinux 9 1:3.5.5-4.el9_8

almalinux advisories ALSA-2026:25237ALSA-2026:25239

  • openssl Rocky Linux 10 1:3.5.5-4.el10_2
  • openssl Rocky Linux 9 1:3.5.5-4.el9_8

rocky linux advisories RLSA-2026:25237RLSA-2026:25239

  • openssl Alpine 3.21 3.3.7-r1
  • openssl Alpine 3.24, Alpine 3.23, Alpine 3.22 3.5.7-r0

alpine advisories ALPINE-CVE-2026-42768

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • openssl Azure Linux 3.0 3.3.7-3

azure linux advisories AZL-90090

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-42768 updated cvss 6.3

openssl: Multi-RecipientInfo Bleichenbacher Oracle in CMS_decrypt() and PKCS7_decrypt()

  • Red Hat Enterprise Linux 6 openssl, openssl-perl Red Hat Enterprise Linux 7 ovmf, OVMF, AAVMF Red Hat Enterprise Linux 8 edk2, shim, openssl, shim-x64, edk2-ovmf, shim-aa64, +9 more Red Hat Enterprise Linux 9 edk2, shim, shim-x64, edk2-ovmf, shim-aa64, edk2-tools, +4 more Red Hat Enterprise Linux 10 edk2, shim, shim-unsigned-x64, shim-unsigned-aarch64 Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.17 cert-manager/cert-manager-operator-rhel9 1791788287, cert-manager/jetstack-cert-manager-rhel9 1791371069, cert-manager/cert-manager-operator-bundle 1791970484, cert-manager/jetstack-cert-manager-acmesolver-rhel9 1791371080
    fixed: vendor fix RHSA-2026:82888
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.18 cert-manager/cert-manager-operator-rhel9 1789029076, cert-manager/jetstack-cert-manager-rhel9 1791459711, cert-manager/cert-manager-istio-csr-rhel9 1791459759, cert-manager/cert-manager-operator-bundle 1791966259, cert-manager/jetstack-cert-manager-acmesolver-rhel9 1791459707
    fixed: vendor fix RHSA-2026:82354
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/cert-manager-trust-manager-rhel9 1790598593
    fixed: vendor fix RHSA-2026:72502
  • Red Hat Discovery 2 discovery/discovery-ui-rhel9 1782166952, discovery/discovery-server-rhel9 1782159791
    fixed: vendor fix RHSA-2026:29197
  • Red Hat Enterprise Linux AppStream (v. 9) openssl-perl 3.5.5-4.el9_8
    fixed: vendor fix RHSA-2026:25239
  • Red Hat Enterprise Linux AppStream (v. 10) openssl-perl 3.5.5-4.el10_2
    fixed: vendor fix RHSA-2026:25237
  • Red Hat Enterprise Linux BaseOS (v. 9) openssl 3.5.5-4.el9_8, openssl-libs 3.5.5-4.el9_8
    fixed: vendor fix RHSA-2026:25239
show 5 more
  • Red Hat Enterprise Linux BaseOS (v. 10) openssl 3.5.5-4.el10_2, openssl-libs 3.5.5-4.el10_2
    fixed: vendor fix RHSA-2026:25237
  • Red Hat Hardened Images bootupd 0.3.2-1.hum1, chunkah 0.6.0-3.hum1, openssl 3.5.8-0.1.hum1, openssl3 3.5.8-0.1.hum1, ruby4.0 4.0.6-37.3.hum1, ruby3.3 3.3.10-23.6.hum1, +20 more
    fixed: vendor fix RHSA-2026:67551
  • Red Hat Insights proxy 1.5 insights-proxy/insights-proxy-container-rhel9 1782890503
    fixed: vendor fix RHSA-2026:34102
  • Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1781525684, rhui5/rhua-rhel9 1781525739, rhui5/haproxy-rhel9 1781525671, rhui5/rhua-tp-rhel9 1787241260, rhui5/installer-rhel9 1781525693, rhui5/installer-tp-rhel9 1787135742, +1 more
    fixed: vendor fix RHSA-2026:58981
  • Red Hat Hardened Images rust, unbound, netavark, openshell, rust-podman-sequoia, rubygem3.3-rbs 3.4.0-23.6.hum1, +50 more Red Hat JBoss Core Services jbcs-httpd24-openssl, jbcs-httpd24-openssl-libs, jbcs-httpd24-openssl-perl, jbcs-openssl-win6-x86_64.zip 3.5.5-SP4 Red Hat JBoss Web Server 6 jws-optional-native-components-win6-x86_64.zip 6.2.4.ER1 Red Hat JBoss Web Server 7 jws-optional-native-components-win6-x86_64.zip 6.2.4.ER1 Red Hat Update Infrastructure 5 rhui5/cds-tp-rhel9 1787241206, rhui5/cds-kubernetes-rhel9 1781525677
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
5 mo ago

Exploit prediction

0.80% chance of exploitation in the next 30 days, higher than 56% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
OSV 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Affected packages

ecosystem package affected fixed in
julia AppBundler
>=1.0.0, <1.0.1
1.0.1
julia OpenSSL_jll
>=3.5.0+0, <3.5.7+0
3.5.7+0
julia Openresty_jll
>=1.29.203+0
 no fix listed

Affected products

  • OpenSSL OpenSSL

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.