Bleichenbacher Oracle in OpenSSL CMS_decrypt() and PKCS7_decrypt()
CVE-2026-42768 is a low-severity Bleichenbacher-style adaptive chosen-ciphertext oracle in OpenSSL's CMS_decrypt() and PKCS7_decrypt() functions when processing CMS or S/MIME messages that use RSA PKCS#1 v1.5 Key Transport. The issue affects OpenSSL 4.0.0 before 4.0.1, 3.6.0 before 3.6.3, 3.5.0 before 3.5.7, and 3.4.0 before 3.4.6. In one variant, when the decryption API is used without supplying the recipient certificate, OpenSSL iterates over all KeyTransRecipientInfo entries instead of stopping at the first success. An attacker can craft a message containing two KTRI entries, with one valid wrapped CEK and one attacker-controlled probe ciphertext, and use distinguishable error behavior to test PKCS#1 v1.5 padding validity. In the second variant, when a recipient certificate is supplied but no matching recipient is found, OpenSSL substitutes a random key; if an attacker can compare both the error code and decryption result, this also creates an oracle condition. The flaw arises from observable differences in error handling and decryption behavior during RSA PKCS#1 v1.5 key transport processing.
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Impact, mitigation & remediation
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Impact
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Mitigation
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Remediation
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Exploits
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No public exploit code observed for this vulnerability.
Affected products & vendors
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Recent activity
22 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An OpenSSL vulnerability addressed in Alpine Linux 3.22.5 and 3.23.5 as part of the June 9, 2026 OpenSSL advisory.
An OpenSSL vulnerability addressed in Alpine Linux 3.24.1 as part of the June 9, 2026 advisory.
A low-severity OpenSSL Bleichenbacher-style oracle vulnerability in CMS_decrypt() and PKCS7_decrypt() that can enable decryption or signing with a victim's private RSA key under narrow conditions.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.