From 045cede1b88195ab9ed0e3458aef9bdab48d4882 Mon Sep 17 00:00:00 2001 From: Gilles Peskine Date: Tue, 12 May 2026 17:21:48 +0200 Subject: [PATCH] basicConstraints with leading INTEGER field: document the behavior change Announce the security fix together with the overflow fix, since the two bugs are pretty much indistinguishable from a black-box perspective, despite being due to independent problems in the code. Signed-off-by: Gilles Peskine --- ChangeLog.d/x509-crt-parse-basicConstraints.txt | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/ChangeLog.d/x509-crt-parse-basicConstraints.txt b/ChangeLog.d/x509-crt-parse-basicConstraints.txt index c5b25f114b..4fd450e18e 100644 --- a/ChangeLog.d/x509-crt-parse-basicConstraints.txt +++ b/ChangeLog.d/x509-crt-parse-basicConstraints.txt @@ -1,7 +1,15 @@ Security - * Fix a bug in the X.509 certificate parser that caused some inputs + * Fix two bugs in the X.509 certificate parser that caused some inputs with a malformed basicConstraints extension to be accepted. This could have dangerous results, in particular causing some certificates to be parsed as CA certificates when other X.509 implementations would parse them as end-entity certificates. Reported by Mohammad Seet (mhdsait101). CVE-2026-TODO + +Changes + * X.509 certificates with a basicConstraints extension starting with an + INTEGER field are no longer accepted. According to RFC 5280, such + certificates are syntactically valid and the first field is the + pathLenConstraint value, but certificate authorities must not emit such + certificates. Mbed TLS interpreted it as a cA value, which was nonstandard + and dangerous.