GHSA-5m8f-m8jv-3rp3 · Severity: low — Issue summary: The CMS_decrypt and PKCS7_decrypt functions are vulnerable to Bleichenbacher-style...
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.
Conclusion & alert: CVE-2026-42768 is rated Low Risk (24.5/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.35%). Mandatory action: Monitor for updates and reassess as exploit intelligence or EPSS changes.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-06-15 | 0.01% | 0.35% | +0.34% |
| 2 | 2026-06-10 | — | 0.01% | — |
Full EPSS history (2 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 3.7 | 3.1 | LOW |
|
2.2 | 1.4 | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
GHSA-5m8f-m8jv-3rp3 · Severity: low — Issue summary: The CMS_decrypt and PKCS7_decrypt functions are vulnerable to Bleichenbacher-style...
| vendor | priority | summary | link |
|---|---|---|---|
debian
|
unimportant | CVE-2026-42768 unimportant priority: Debian including 1 source packages (openssl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. | https://security-tracker.debian.org/tracker/CVE-2026-42768 |
redhat
|
low | — | https://access.redhat.com/security/cve/CVE-2026-42768 |
suse
|
medium | CVE-2026-42768 severity moderate: SUSE including 49 source package names (compat-openssl098, libopenssl-1_0_0-devel, …), 281 product×package rows across 35 product lines (SUSE Liberty Linux 10, SUSE Liberty Linux 9, … (35 product lines)): Known Not Affected 267, Fixed 8, First Fixed 6. | https://www.suse.com/security/cve/CVE-2026-42768/ |
ubuntu
|
low | CVE-2026-42768 low priority: Ubuntu including 5 source packages (edk2, nodejs, openssl, openssl-fips, openssl1.0), 35 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): not-affected 19, needs-triage 7, DNE 6, released 2, needed 1. | https://ubuntu.com/security/CVE-2026-42768 |
| Vendor | Product | Version | Raw CPE |
|---|---|---|---|
| openssl | openssl | >= 3.4.0, < 3.4.6 | cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* |
| openssl | openssl | >= 3.5.0, < 3.5.7 | cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* |
| openssl | openssl | >= 3.6.0, < 3.6.3 | cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* |
| openssl | openssl | 4.0.0 | cpe:2.3:a:openssl:openssl:4.0.0:-:*:*:*:*:*:* |