diff --git a/ChangeLog b/ChangeLog
index f01cab9..024d564 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -9,6 +9,8 @@
      a crash on invalid input.
    * Fix a buffer overread in ssl_parse_server_psk_hint() that could cause a
      crash on invalid input.
+   * Fix CRL parsing to reject CRLs containing unsupported critical
+     extensions. Found by Falko Strenzke and Evangelos Karatsiolis.
 
 Features
    * Extend PKCS#8 interface by introducing support for the entire SHA
diff --git a/library/x509_crl.c b/library/x509_crl.c
index 0bb7236..b0f39d4 100644
--- a/library/x509_crl.c
+++ b/library/x509_crl.c
@@ -95,17 +95,23 @@
 }
 
 /*
- * X.509 CRL v2 extensions (no extensions parsed yet.)
+ * X.509 CRL v2 extensions
+ *
+ * We currently don't parse any extension's content, but we do check that the
+ * list of extensions is well-formed and abort on critical extensions (that
+ * are unsupported as we don't support any extension so far)
  */
 static int x509_get_crl_ext( unsigned char **p,
                              const unsigned char *end,
                              mbedtls_x509_buf *ext )
 {
     int ret;
-    size_t len = 0;
 
-    /* Get explicit tag */
-    if( ( ret = mbedtls_x509_get_ext( p, end, ext, 0) ) != 0 )
+    /*
+     * crlExtensions           [0]  EXPLICIT Extensions OPTIONAL
+     *                              -- if present, version MUST be v2
+     */
+    if( ( ret = mbedtls_x509_get_ext( p, end, ext, 0 ) ) != 0 )
     {
         if( ret == MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
             return( 0 );
@@ -115,11 +121,54 @@
 
     while( *p < end )
     {
+        /*
+         * Extension  ::=  SEQUENCE  {
+         *      extnID      OBJECT IDENTIFIER,
+         *      critical    BOOLEAN DEFAULT FALSE,
+         *      extnValue   OCTET STRING  }
+         */
+        int is_critical = 0;
+        const unsigned char *end_ext_data;
+        size_t len;
+
+        /* Get enclosing sequence tag */
         if( ( ret = mbedtls_asn1_get_tag( p, end, &len,
                 MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
             return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
 
+        end_ext_data = *p + len;
+
+        /* Get OID (currently ignored) */
+        if( ( ret = mbedtls_asn1_get_tag( p, end_ext_data, &len,
+                                          MBEDTLS_ASN1_OID ) ) != 0 )
+        {
+            return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
+        }
         *p += len;
+
+        /* Get optional critical */
+        if( ( ret = mbedtls_asn1_get_bool( p, end_ext_data,
+                                           &is_critical ) ) != 0 &&
+            ( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG ) )
+        {
+            return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
+        }
+
+        /* Data should be octet string type */
+        if( ( ret = mbedtls_asn1_get_tag( p, end_ext_data, &len,
+                MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
+            return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS + ret );
+
+        /* Ignore data so far and just check its length */
+        *p += len;
+        if( *p != end_ext_data )
+            return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
+                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
+
+        /* Abort on (unsupported) critical extensions */
+        if( is_critical )
+            return( MBEDTLS_ERR_X509_INVALID_EXTENSIONS +
+                    MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
     }
 
     if( *p != end )
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 049e8cf..df4834d 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -46,6 +46,13 @@
 	$(OPENSSL) req -x509 -config $(test_ca_config_file) -key $(test_ca_key_file_rsa) -passin "pass:$(test_ca_pwd_rsa)" -set_serial 0 -days 3653 -sha256 -in test-ca.csr -out $@
 all_final += test-ca-sha256.crt
 
+crl-idp.pem: $(test_ca_crt) $(test_ca_key_file_rsa) $(test_ca_config_file)
+	$(OPENSSL) ca -gencrl -batch -cert $(test_ca_crt) -keyfile $(test_ca_key_file_rsa) -key $(test_ca_pwd_rsa) -config $(test_ca_config_file) -name test_ca -md sha256 -crldays 3653 -crlexts crl_ext_idp -out $@
+all_final += crl-idp.pem
+crl-idpnc.pem: $(test_ca_crt) $(test_ca_key_file_rsa) $(test_ca_config_file)
+	$(OPENSSL) ca -gencrl -batch -cert $(test_ca_crt) -keyfile $(test_ca_key_file_rsa) -key $(test_ca_pwd_rsa) -config $(test_ca_config_file) -name test_ca -md sha256 -crldays 3653 -crlexts crl_ext_idp_nc -out $@
+all_final += crl-idpnc.pem
+
 cli_crt_key_file_rsa = cli-rsa.key
 cli_crt_extensions_file = cli.opensslconf
 
diff --git a/tests/data_files/crl-idp.pem b/tests/data_files/crl-idp.pem
new file mode 100644
index 0000000..a229e7d
--- /dev/null
+++ b/tests/data_files/crl-idp.pem
@@ -0,0 +1,12 @@
+-----BEGIN X509 CRL-----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+-----END X509 CRL-----
diff --git a/tests/data_files/crl-idpnc.pem b/tests/data_files/crl-idpnc.pem
new file mode 100644
index 0000000..0ebe480
--- /dev/null
+++ b/tests/data_files/crl-idpnc.pem
@@ -0,0 +1,12 @@
+-----BEGIN X509 CRL-----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+-----END X509 CRL-----
diff --git a/tests/data_files/test-ca.opensslconf b/tests/data_files/test-ca.opensslconf
index 12835df..571d96e 100644
--- a/tests/data_files/test-ca.opensslconf
+++ b/tests/data_files/test-ca.opensslconf
@@ -11,3 +11,15 @@
 subjectKeyIdentifier=hash
 authorityKeyIdentifier=keyid:always,issuer:always
 basicConstraints = CA:true
+
+[test_ca]
+database = /dev/null
+
+[crl_ext_idp]
+issuingDistributionPoint=critical, @idpdata
+
+[crl_ext_idp_nc]
+issuingDistributionPoint=@idpdata
+
+[idpdata]
+fullname=URI:http://pki.example.com/
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index 8e17163..3fc017b 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -202,6 +202,14 @@
 depends_on:MBEDTLS_PEM_PARSE_C
 mbedtls_x509_crl_parse:"data_files/crl-malformed-trailing-spaces.pem":MBEDTLS_ERR_PEM_NO_HEADER_FOOTER_PRESENT
 
+X509 CRL Unsupported critical extension (issuingDistributionPoint)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
+mbedtls_x509_crl_parse:"data_files/crl-idp.pem":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_UNEXPECTED_TAG
+
+X509 CRL Unsupported non-critical extension (issuingDistributionPoint)
+depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_RSA_C:MBEDTLS_SHA256_C
+mbedtls_x509_crl_parse:"data_files/crl-idpnc.pem":0
+
 X509 CSR Information RSA with MD4
 depends_on:MBEDTLS_PEM_PARSE_C:MBEDTLS_MD4_C
 mbedtls_x509_csr_info:"data_files/server1.req.md4":"CSR version   \: 1\nsubject name  \: C=NL, O=PolarSSL, CN=PolarSSL Server 1\nsigned using  \: RSA with MD4\nRSA key size  \: 2048 bits\n"
@@ -1218,6 +1226,24 @@
 X509 CRL ASN1 (invalid version overflow)
 x509parse_crl:"3049303102047FFFFFFF300d06092a864886f70d01010e0500300f310d300b0603550403130441424344170c303930313031303030303030300d06092a864886f70d01010e050003020001":"":MBEDTLS_ERR_X509_UNKNOWN_VERSION
 
+X509 CRL ASN1 (extension seq too long, crl-idp.pem byte 121)
+x509parse_crl:"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":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_OUT_OF_DATA
+
+X509 CRL ASN1 (extension oid too long, crl-idp.pem byte 123)
+x509parse_crl:"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":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_OUT_OF_DATA
+
+X509 CRL ASN1 (extension critical invalid length, crl-idp.pem byte 128)
+x509parse_crl:"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":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_INVALID_LENGTH
+
+X509 CRL ASN1 (extension data too long, crl-idp.pem byte 131)
+x509parse_crl:"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":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_OUT_OF_DATA
+
+X509 CRL ASN1 (extension data too short, crl-idp.pem byte 131)
+x509parse_crl:"308201b330819c020101300d06092a864886f70d01010b0500303b310b3009060355040613024e4c3111300f060355040a1308506f6c617253534c3119301706035504031310506f6c617253534c2054657374204341170d3138303331343037333134385a170d3238303331343037333134385aa02d302b30290603551d1c0101ff041e301da01ba0198617687474703a2f2f706b692e6578616d706c652e636f6d2f300d06092a864886f70d01010b05000382010100b3fbe9d586eaf4b8ff60cf8edae06a85135db78f78198498719725b5b403c0b803c2c150f52faae7306d6a7871885dc2e9dc83a164bac7263776474ef642b660040b35a1410ac291ac8f6f18ab85e7fd6e22bd1af1c41ca95cf2448f6e2b42a018493dfc03c6b6aa1b9e3fe7b76af2182fb2121db4166bf0167d6f379c5a58adee5082423434d97be2909f5e7488053f996646db10dd49782626da53ad8eada01813c031b2bacdb0203bc017aac1735951a11d013ee4d1d5f7143ccbebf2371e66a1bec6e1febe69148f50784eef8adbb66664c96196d7e0c0bcdc807f447b54e058f37642a3337995bfbcd332208bd6016936705c82263eabd7affdba92fae3":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS + MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
+
+X509 CRL ASN1 (extension not critical explicit, crl-idp.pem byte 129)
+x509parse_crl:"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":"CRL version   \: 2\nissuer name   \: C=NL, O=PolarSSL, CN=PolarSSL Test CA\nthis update   \: 2018-03-14 07\:31\:48\nnext update   \: 2028-03-14 07\:31\:48\nRevoked certificates\:\nsigned using  \: RSA with SHA-256\n":0
+
 X509 CRT parse path #2 (one cert)
 depends_on:MBEDTLS_SHA1_C:MBEDTLS_RSA_C
 mbedtls_x509_crt_parse_path:"data_files/dir1":0:1