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() handling of RSA PKCS#1 v1.5 Key Transport in CMS/S/MIME messages. 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 legitimate wrapped CEK and one probe ciphertext, and use application-visible 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. The flaw arises from distinguishable decryption behavior around RSA PKCS#1 v1.5 processing, enabling Bleichenbacher-style probing against the victim's private RSA key operations.
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Impact
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Mitigation
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Remediation
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Exploits
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Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An OpenSSL vulnerability addressed in Alpine Linux 3.24.1 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.