LibCrypto: Don't crash in ASN1::parse_utc_time on missing 'Z'

The underlying reason is an unconditional call to consume(), even if
there is no reason to expect that the string continues.

This crash was discovered by OSS-Fuzz:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=42354
This bug exists since the code was first written in April 2021:
13abbc5ea8c6b0bb145983c7d232dbe3bdc398c3

2 files changed, 20 insertions, 22 deletions

diff --git a/Tests/LibCrypto/TestASN1.cpp b/Tests/LibCrypto/TestASN1.cpp
index 6c766b787e..e18b61174d 100644
--- a/Tests/LibCrypto/TestASN1.cpp
+++ b/Tests/LibCrypto/TestASN1.cpp
@@ -57,10 +57,9 @@ TEST_CASE(test_utc_missing_z)
     // YYMMDDhhmm[ss]
     // We don't actually need to parse this correctly; rejecting these inputs is fine.
     // This test just makes sure that we don't crash.
-    // FIXME: This currently crashes
-    // (void)Crypto::ASN1::parse_utc_time("010101010101"sv);
-    // (void)Crypto::ASN1::parse_utc_time("010203040506"sv);
-    // (void)Crypto::ASN1::parse_utc_time("020406081012"sv);
-    // (void)Crypto::ASN1::parse_utc_time("0204060810"sv);
-    // (void)Crypto::ASN1::parse_utc_time("220911220000"sv);
+    (void)Crypto::ASN1::parse_utc_time("010101010101"sv);
+    (void)Crypto::ASN1::parse_utc_time("010203040506"sv);
+    (void)Crypto::ASN1::parse_utc_time("020406081012"sv);
+    (void)Crypto::ASN1::parse_utc_time("0204060810"sv);
+    (void)Crypto::ASN1::parse_utc_time("220911220000"sv);
 }
diff --git a/Userland/Libraries/LibCrypto/ASN1/ASN1.cpp b/Userland/Libraries/LibCrypto/ASN1/ASN1.cpp
index 8acf1f37f0..a585646293 100644
--- a/Userland/Libraries/LibCrypto/ASN1/ASN1.cpp
+++ b/Userland/Libraries/LibCrypto/ASN1/ASN1.cpp
@@ -84,26 +84,25 @@ Optional<Core::DateTime> parse_utc_time(StringView time)
     auto minute = lexer.consume(2).to_uint();
     Optional<unsigned> seconds, offset_hours, offset_minutes;
     [[maybe_unused]] bool negative_offset = false;
-    if (!lexer.next_is('Z')) {
-        if (!lexer.next_is(is_any_of("+-"sv))) {
-            seconds = lexer.consume(2).to_uint();
-            if (!seconds.has_value()) {
-                return {};
-            }
+
+    if (lexer.next_is(is_any_of("0123456789"sv))) {
+        seconds = lexer.consume(2).to_uint();
+        if (!seconds.has_value()) {
+            return {};
         }
+    }
 
-        if (lexer.next_is(is_any_of("+-"sv))) {
-            negative_offset = lexer.consume() == '-';
-            offset_hours = lexer.consume(2).to_uint();
-            offset_minutes = lexer.consume(2).to_uint();
-            if (!offset_hours.has_value() || !offset_minutes.has_value()) {
-                return {};
-            }
-        } else {
-            lexer.consume();
+    if (lexer.next_is('Z')) {
+        lexer.consume();
+    } else if (lexer.next_is(is_any_of("+-"sv))) {
+        negative_offset = lexer.consume() == '-';
+        offset_hours = lexer.consume(2).to_uint();
+        offset_minutes = lexer.consume(2).to_uint();
+        if (!offset_hours.has_value() || !offset_minutes.has_value()) {
+            return {};
         }
     } else {
-        lexer.consume();
+        return {};
     }
 
     if (!year_in_century.has_value() || !month.has_value() || !day.has_value() || !hour.has_value() || !minute.has_value()) {