From 5b535a091b919dfe696485f9ce2c188c1f426438 Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Tue, 12 May 2026 13:16:26 +0200
Subject: [PATCH] Add test certificate with basicConstraints containing only an
 INTEGER

The basicConstraints extension contains only an INTEGER. According to
RFC 5280, this should be cA=FALSE and a pathLenConstraint value which is
effectively ignored. But Mbed TLS parses it as cA=TRUE if the integer value
is nonzero.

This certificate is syntactically valid, but RFC 5280 forbids CAs from
emitting it. Compliant X.509 parsers treat it as cA=FALSE.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
---
 data_files/Makefile                             |  16 ++++++++++++++++
 ....basic-constraints-integer-first.badsign.crt | Bin 0 -> 461 bytes
 ...sic-constraints-integer-first.selfsigned.crt | Bin 0 -> 347 bytes
 3 files changed, 16 insertions(+)
 create mode 100644 data_files/parse_input/server5.basic-constraints-integer-first.badsign.crt
 create mode 100644 data_files/parse_input/server5.basic-constraints-integer-first.selfsigned.crt

diff --git a/data_files/Makefile b/data_files/Makefile
index 4a1b03f63..5a379a99a 100644
--- a/data_files/Makefile
+++ b/data_files/Makefile
@@ -2328,6 +2328,22 @@ parse_input/server5.basic-constraints-sequence-overflow.selfsigned.crt: parse_in
 		-inform DER -in $< -outform DER -out $@
 all_final += parse_input/server5.basic-constraints-sequence-overflow.selfsigned.crt
 
+# Replace a well-formed basicConstraints extension containing CA:TRUE with
+# a malformed extension that is empty with trailing junk. The trailing
+# junk is a boolean with the value true, thus it would be interpreted as
+# CA:TRUE if it was properly inside the basicConstraints extension.
+parse_input/server5.basic-constraints-integer-first.badsign.crt: server5-ca.der
+	perl -0777 -pe '$$n = s/\x04\x05\x30\x03\x01\x01\xff/\x04\x05\x30\x03\x02\x01\x01/g; die "More substitutions than expected" if $$n > 1; die "Substitution not found" if $$n < 1' <$< >$@.tmp
+	mv $@.tmp $@
+all_final += parse_input/server5.basic-constraints-integer-first.badsign.crt
+
+parse_input/server5.basic-constraints-integer-first.selfsigned.crt: parse_input/server5.basic-constraints-integer-first.badsign.crt server5.key
+	$(OPENSSL) x509 -subj '/CN=Eve/' \
+		-key server5.key \
+		-days 3653 \
+		-inform DER -in $< -outform DER -out $@
+all_final += parse_input/server5.basic-constraints-integer-first.selfsigned.crt
+
 # MD5 test certificate
 
 cert_md_test_key = $(cli_crt_key_file_rsa)
diff --git a/data_files/parse_input/server5.basic-constraints-integer-first.badsign.crt b/data_files/parse_input/server5.basic-constraints-integer-first.badsign.crt
new file mode 100644
index 0000000000000000000000000000000000000000..75d734a9a3a135c6c92aa791406ce642b0cb9272
GIT binary patch
literal 461
zcmXqLVmxWk#8|L^nTe5!i6?l`X>TFFwav9Frff3cV&l+i^EhYA!pvmgZYXRZ$i^JX
z!py@}oSKtXoSB}Nnqnwmzy}iK=3y^MEiTE-OE(lW;0K9t@o)s>=Oh*d2m2Uu8*qYz
z*o2w<d<^8od5z2rObyHpO@X9wlsK<3h-(7nQqQ7D17S9Hu=|-9p&nsoWM_6_U@<=v
zcC(CAE~?1xc%<%sg}iq)KiMXhTv#iz^?Qa=WYQ$Rrwlig1^>U&zhn{{E4H_*<4|@v
zZ|K=BExuojC$_x(zu3vZ0qjdzVMfOPEUX5=uww)Vge*Tu02p5E4F<A6Kg;s5h_Q$S
zBrfg0!hZ956C=;l)cT%ex8=h7kOP<5ox#9`Nx^ULBI^goIC3KcK4*P&I2Zj(_V7M;
z@tIte2?yjX8p=O1DRA`|Pl}x0V;;XCbaT~|3A6WGSeN>nzYq4k_a}Xltf~S4(W8a<

literal 0
HcmV?d00001

diff --git a/data_files/parse_input/server5.basic-constraints-integer-first.selfsigned.crt b/data_files/parse_input/server5.basic-constraints-integer-first.selfsigned.crt
new file mode 100644
index 0000000000000000000000000000000000000000..d57fe4a21e80f6ba9ffa3e18a112c1f6bb07ee5f
GIT binary patch
literal 347
zcmXqLVhlHE{I`IaiIItkCwS3mZy~?6&9y70Y%<_t<IrmJIA_bk%w)i4$OGgvhq5s9
zFuRte8pw(B8krfG8X6f`ni?CJM2YhnBXcp-M;ZvTv4c%xVuTvY%*f8{#K2;HChTSz
zr(9H#-SJ4>{|b5UYJRd!EV-~&Wb5|~rO2d7eoq;0C=337rGLpJHdbtJSI433a^BFh
zU0Qs<7*A|@`+u>Mfr9}*&}p*5jEw(TSPg(aVKm?a3GjmifUak6FpvfD`B=nQL;@0*
z_FrMYdA*5|=V@wvPqN!`;eE(nW%gh&aAi_txK<mk^<h;A&xM~ia-A!B#Cui-$oBC2
xr%gCs{AGuZ_bes_!6g27&$Lciy6i9#Gi#Y(!07jbjU|-9&`^6j`}R-!SpWrvX~h5l

literal 0
HcmV?d00001