# What Is OCSP Must-Staple (TLS Feature extension)?

> OCSP Must-Staple is a certificate extension telling clients to reject the certificate if the server does not staple a valid OCSP response.

Source: https://ssl.sh/glossary/must-staple/
Last updated: 2026-11-10

OCSP Must-Staple is an X.509 extension, formally the TLS Feature extension from [RFC 7633](https://www.rfc-editor.org/rfc/rfc7633), whose value lists status_request. It is a promise from the certificate holder that every TLS server using this certificate will provide a stapled [OCSP](https://ssl.sh/glossary/ocsp/) response, so a client may treat a missing staple as a hard failure instead of silently continuing.

## Why it matters
Must-Staple was the main attempt to turn OCSP's soft-fail behavior into hard-fail without making every browser query the CA. In practice support stayed narrow: Firefox enforces it and shows an error when the staple is missing, while Chrome ignores the extension. Operating it is fragile, because a responder outage, or a web server that has not yet fetched a response, makes the site unreachable for enforcing clients. The industry has since moved away from OCSP: Ballot SC-063 made OCSP optional for CAs, and Let's Encrypt began rejecting Must-Staple requests on 2025-05-07, when it removed OCSP URLs from new certificates.

## Example
Check whether a certificate carries the extension:

```bash
openssl x509 -in cert.pem -noout -text | grep -A1 "TLS Feature"
```

A Must-Staple certificate shows `TLS Feature:` followed by `status_request`. No output means the extension is absent.

## Common misconceptions
- **Must-Staple is a server setting.** It is written into the certificate at issuance; the server must then be configured separately for [OCSP stapling](https://ssl.sh/glossary/ocsp-stapling/).
- **All browsers enforce it.** Chrome does not; enforcement has been mostly limited to Firefox.
- **It is still a recommended hardening step.** With CAs dropping OCSP, a Must-Staple certificate can no longer be obtained from Let's Encrypt; shorter certificate lifetimes and browser-side revocation lists are the current direction.

## Related terms

- [OCSP Stapling](https://ssl.sh/zh/glossary/ocsp-stapling/): OCSP Stapling 是 TLS 服务器把 CA 签名、带有效期的 OCSP 响应随握手一起发给客户端的机制，浏览器因此不必再自己去问 CA。
- [OCSP](https://ssl.sh/zh/glossary/ocsp/): OCSP 是 RFC 6960 定义的在线证书状态协议，客户端可以向 CA 的响应服务器查询某一张证书当前是有效、已吊销还是未知。
- [证书吊销](https://ssl.sh/zh/glossary/revocation/): 证书吊销是 CA 在证书到期前宣布其作废的操作，通过 CRL 或 OCSP 对外公布，使客户端不再信任这张证书。
- [X.509](https://ssl.sh/zh/glossary/x509/): X.509 是 ITU-T 制定的公钥证书标准格式，其互联网配置规范 RFC 5280 规定了 TLS 所用证书的结构和验证方法。
- [TLS 握手](https://ssl.sh/zh/glossary/tls-handshake/): TLS 握手是 TLS 连接开始时的一组消息交换，客户端与服务器在其中协商协议版本和密码套件、验证服务器身份并派生会话密钥。
- [CRL](https://ssl.sh/zh/glossary/crl/): CRL 是由 CA 签名并定期重新发布的证书吊销列表，列出它在证书到期前就已吊销的证书序列号。