From 242d1d8ebaee9e519eddc11c6af2666679e76d8c Mon Sep 17 00:00:00 2001
From: Daniel La Rocque <larocq17@myumanitoba.ca>
Date: Fri, 5 Jan 2024 09:56:14 -0500
Subject: [PATCH] LibWeb: Fail to parse cookie date when date does not exist

Previously, the cookie date validation did not validate days in the
context of the month and year, resulting in dates that do not exist to
be successfully parsed (e.g. February 31st). We now validate that the
day does not exceed the number of days for the given month and year,
taking leap years into account.
---
 Base/res/html/misc/cookie.html                    | 2 ++
 Userland/Libraries/LibWeb/Cookie/ParsedCookie.cpp | 4 +++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Base/res/html/misc/cookie.html b/Base/res/html/misc/cookie.html
index 3ab6fb7721..f4a5cf4ab1 100644
--- a/Base/res/html/misc/cookie.html
+++ b/Base/res/html/misc/cookie.html
@@ -22,6 +22,8 @@
     <label for=invalid5>The cookie is too large</label>
     <br /><input id=invalid6 type=button onclick="setCookie(this.value)" value="cookie11=value11; domain=uk.gov" />
     <label for=invalid6>The cookie's domain is on the Public Suffix List</label>
+    <br /><input id=invalid7 type=button onclick="setCookie(this.value)" value="cookie12=value12; expires=Sat, 31 Feb 2060 08:10:36 GMT" />
+    <label for=invalid4>The cookie has a date that does not exist</label>
     <br />
 
     <h3>Unretrievable cookies (the browser should accept these but not display them):</h3>
diff --git a/Userland/Libraries/LibWeb/Cookie/ParsedCookie.cpp b/Userland/Libraries/LibWeb/Cookie/ParsedCookie.cpp
index 3729947ab3..2c171c377b 100644
--- a/Userland/Libraries/LibWeb/Cookie/ParsedCookie.cpp
+++ b/Userland/Libraries/LibWeb/Cookie/ParsedCookie.cpp
@@ -345,7 +345,9 @@ Optional<UnixDateTime> parse_date_time(StringView date_string)
     // 6. Let the parsed-cookie-date be the date whose day-of-month, month, year, hour, minute, and second (in UTC) are the
     //    day-of-month-value, the month-value, the year-value, the hour-value, the minute-value, and the second-value, respectively.
     //    If no such date exists, abort these steps and fail to parse the cookie-date.
-    // FIXME: Fail on dates that do not exist.
+    if (day_of_month > static_cast<unsigned int>(days_in_month(year, month)))
+        return {};
+
     // FIXME: This currently uses UNIX time, which is not equivalent to UTC due to leap seconds.
     auto parsed_cookie_date = UnixDateTime::from_unix_time_parts(year, month, day_of_month, hour, minute, second, 0);