# CVE-2026-42768: Multi-RecipientInfo Bleichenbacher Oracle in CMS_decrypt() and PKCS7_decrypt()

> Attackers can exploit a Bleichenbacher oracle in OpenSSL's CMS/PKCS7 decryption to decrypt messages or forge signatures using the victim's private RSA key.

- **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Jun 2026
- **Updated:** 10 Jun 2026
- **Also known as:** ALPINE-CVE-2026-42768, AZL-90090, BELL-CVE-2026-42768, DEBIAN-CVE-2026-42768, GHSA-5m8f-m8jv-3rp3, JLSEC-2026-1140, MINI-7hwv-2fw6-6jwr, UBUNTU-CVE-2026-42768

## What is CVE-2026-42768?

CVE-2026-42768 is a low-severity vulnerability in Openssl Openssl, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-514 (Covert Channel)

## Which versions are affected by CVE-2026-42768?

It affects 1 product.


Products: Openssl Openssl.

## How do I fix CVE-2026-42768?

Apply the vendor's patch.

## Is CVE-2026-42768 being exploited?

There is no known exploitation of CVE-2026-42768 in the wild and no public exploit code.

## Other vulnerabilities in Openssl Openssl

- [CVE-2009-3245](https://insights.sbomify.com/CVE-2009-3245/): Null dereference in n/a (critical 10.0)
- [CVE-2006-3738](https://insights.sbomify.com/CVE-2006-3738/): Memory corruption in n/a (critical 10.0)
- [CVE-2026-63073](https://insights.sbomify.com/CVE-2026-63073/): Untrusted Sender DN Used as Format String in CMP Response Validation (critical 9.8)
- [CVE-2016-6309](https://insights.sbomify.com/CVE-2016-6309/): Use after free in n/a (critical 9.8)
- [CVE-2016-0799](https://insights.sbomify.com/CVE-2016-0799/): Integer overflow in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42768 and fix it if it is affected.

What it is: CVE-2026-42768 is a low-severity vulnerability in Openssl Openssl, published on 9 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-42768 in the wild and no public exploit code.

Affected product: Openssl Openssl. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-42768/ (Markdown: https://insights.sbomify.com/CVE-2026-42768/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42768
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42768
- OSV: https://osv.dev/vulnerability/CVE-2026-42768

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42768/
Summaries are generated and may contain mistakes; the official description above is the record.