CVE-2017-3733 — During a renegotiation handshake if the Encrypt-Then-Mac extension is negotiated

During a renegotiation handshake if the Encrypt-Then-Mac extension is negotiated where it was not in the original handshake (or vice-versa) then this can cause OpenSSL 1.1.0 before 1.1.0e to crash (dependent on ciphersuite). Both clients and servers are affected.

01What is this vulnerability?

During a renegotiation handshake if the Encrypt-Then-Mac extension is negotiated where it was not in the original handshake (or vice-versa) then this can cause OpenSSL 1.1.0 before 1.1.0e to crash (dependent on ciphersuite). Both clients and servers are affected.

02Affected products

No structured affected-product list available — see references below for vendor advisories.

03Active exploitation status

Not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog. EPSS is the best forward-looking signal — see the EPSS row above.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Ask SARA in chat to draft a starting detection for this CVE in your stack of choice.

07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2017-05-04T19:29:00.430
• Last modified: 2026-05-13T00:24:29.033

09References

• www.oracle.com — http://www.oracle.com/technetwork/security-advisory/cpujan2018-3236628.html
• www.oracle.com — http://www.oracle.com/technetwork/security-advisory/cpuoct2017-3236626.html
• www.securityfocus.com — http://www.securityfocus.com/bid/96269
• www.securitytracker.com — http://www.securitytracker.com/id/1037846
• github.com — https://github.com/openssl/openssl/commit/4ad93618d26a3ea23d36ad5498ff4f59eff3a4…
• h20566.www2.hpe.com — https://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na…
• www.openssl.org — https://www.openssl.org/news/secadv/20170216.txt
• www.oracle.com — https://www.oracle.com/technetwork/security-advisory/cpuapr2019-5072813.html
• www.oracle.com — http://www.oracle.com/technetwork/security-advisory/cpujan2018-3236628.html
• www.oracle.com — http://www.oracle.com/technetwork/security-advisory/cpuoct2017-3236626.html