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Author christian.heimes
Recipients Talos, christian.heimes, larry, miss-islington, ned.deily, vstinner
Date 2019-01-16.12:42:11
SpamBayes Score -1.0
Marked as misclassified Yes
Message-id <>
The bug is less critical and harder to exploit than I initially thought. td;dr if you have cert validation enabled and only trust public root CAs from CA/B forum, then you are not affected.

The bug is only exploitable under two conditions:
1) The user has disabled TLS/SSL certificate validation *and* calls getpeercert() in 3rd party code.
2) Or the user trusts a CA that does not properly validate end-entity certificates.

When cert validation is enabled, the ssl module will refuse any untrusted certificate during the handshake. The SSLSocket.getpeercert() and SSLObject.getpeercert() methods raise an exception, when the handshake was not successful. Python 2.7 - 3.6 hostname verification code only calls getpeercert() after the cert chain was validated successfully. Python 3.7+ no longer calls getpeercert() for hostname verification. Further more hostname verification can't be enabled when cert validation is disabled.

For publicly trusted CAs governed by CA/B baseline requirements, CRL DPs must by valid URI general names with HTTP links. From CA/Browser Forum Baseline Requirements Version 1.6.2, December 10, 2018, section Subscriber Certificate:

b. cRLDistributionPoints
This extension MAY be present. If present, it MUST NOT be marked critical, and it MUST contain the HTTP URL of the CA’s CRL service.
Date User Action Args
2019-01-16 12:42:12christian.heimessetrecipients: + christian.heimes, vstinner, larry, ned.deily, miss-islington, Talos
2019-01-16 12:42:11christian.heimessetmessageid: <>
2019-01-16 12:42:11christian.heimeslinkissue35746 messages
2019-01-16 12:42:11christian.heimescreate