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From f57392a308817917eaac74aed27d2ceb27aba23d Mon Sep 17 00:00:00 2001
From: Paul Wise <pabs3@bonedaddy.net>
Date: Sun, 30 May 2021 09:51:26 +0800
Subject: [PATCH 3/3] Detect reasonable email headers too
RFC 5322 specifies the syntax of email headers, most header fields are more
restricted though so use a restricted check in case the headers are bogus
parts of the body that happen to match RFC 5322.
Fixes: https://bugs.debian.org/984581
---
src/readpst.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 60 insertions(+)
diff --git a/src/readpst.c b/src/readpst.c
index 6f9455297..fbd90c762 100644
--- a/src/readpst.c
+++ b/src/readpst.c
@@ -1283,6 +1283,65 @@ int header_match(char *header, char*field) {
return 0;
}
+// https://en.wikipedia.org/wiki/Email#Message_header
+// https://www.rfc-editor.org/rfc/rfc5322.html
+// https://www.iana.org/assignments/message-headers/message-headers.xhtml
+int header_is_reasonable(char *header)
+{
+ char *c;
+#define C *c
+
+ // The header must not be NULL
+ if (header) c = header;
+ else return 0;
+
+ // usually the header field name starts with upper-case: A-Z
+ if (C >= 'A' && C <= 'Z') c++;
+ else return 0;
+
+ while(1) {
+ // most header field names use a limited set of characters: - 0-9 A-Z a-z
+ if (
+ (C >= 'A' && C <= 'Z') ||
+ (C >= 'a' && C <= 'z') ||
+ (C >= '0' && C <= '9') ||
+ (C == '-')
+ ) {
+ c++;
+ // the header field name is then terminated with a colon
+ } else if (C == ':') {
+ c++;
+ goto parse_header_field_value;
+ // other characters are an indicator of an invalid header
+ } else {
+ return 0;
+ }
+ }
+
+parse_header_field_value:
+ while(1) {
+ // header field values are printable US-ASCII plus space/tab
+ if (
+ (C >= 33 && C <= 126) ||
+ (C == ' ' || C == '\t')
+ ) {
+ c++;
+ // the header field value is then terminated with CRLF
+ } else if (C == '\r' && *(c+1) == '\n') {
+ c += 2;
+ // the value could continue to the next line though
+ if (C == ' ' || C == '\t') c++;
+ else return 1;
+ // other characters are an indicator of an invalid header
+ } else {
+ return 0;
+ }
+ }
+
+#undef C
+
+}
+
int valid_headers(char *header)
{
// headers are sometimes really bogus - they seem to be fragments of the
@@ -1303,6 +1362,7 @@ int valid_headers(char *header)
if (header_match(header, "X-ASG-Debug-ID: " )) return 1;
if (header_match(header, "X-Barracuda-URL: " )) return 1;
if (header_match(header, "X-x: " )) return 1;
+ if (header_is_reasonable(header)) return 1;
if (strlen(header) > 2) {
DEBUG_INFO(("Ignore bogus headers = %s\n", header));
}
--
2.32.0
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