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fix: Handle "filename*" field in MP header #3239

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fix: Handle "filename*" field in MP header #3239

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cd4905b
Handle "filename*" field in MP header
airween Aug 25, 2024
524a799
Fix string comparison
airween Aug 26, 2024
2b22261
Set MULTIPART_INVALID_QUOTING variable if it is necessary
airween Aug 26, 2024
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55 changes: 52 additions & 3 deletions apache2/msc_multipart.c
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,9 @@
#include "msc_util.h"
#include "msc_parsers.h"

static const char* mime_charset_special = "!#$%&+-^_`{}~";
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static const char* attr_char_special = "!#$&+-.^_`~";

void validate_quotes(modsec_rec *msr, char *data, char quote) {
assert(msr != NULL);
int i, len;
Expand Down Expand Up @@ -85,6 +88,7 @@ static int multipart_parse_content_disposition(modsec_rec *msr, char *c_d_value)
assert(msr != NULL);
assert(c_d_value != NULL);
char *p = NULL, *t = NULL;
char *filenameStar = NULL;

/* accept only what we understand */
if (strncmp(c_d_value, "form-data", 9) != 0) {
Expand Down Expand Up @@ -130,7 +134,42 @@ static int multipart_parse_content_disposition(modsec_rec *msr, char *c_d_value)
*/

char quote = '\0';
if ((*p == '"') || (*p == '\'')) {
if (strcmp(name, "filename*") == 0) {
/* filename*=charset'[optional-language]'filename */
/* Read beyond the charset and the optional language*/
const char* start_of_charset = p;
while ((*p != '\0') && (isalnum(*p) || (strchr(mime_charset_special, *p)))) {
p++;
}
if ((*p != '\'') || (p == start_of_charset)) {
return -16; // Must be at least one legit char before ' for start of language
}
p++;
while ((*p != '\0') && (*p != '\'')) {
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Languages can only contain alphanum & '-'
while (isalnum(*p) || *p == '-') p++;

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You're right, and here - as you suggested - we can control this.

The question is: is it allowed to send the request without charset? I mean:

Content-Disposition: form-data; name="post"; filename*=resume.pdf

I can't find any relevant information about that.

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https://www.rfc-editor.org/rfc/rfc7578#section-4.2 also says:

Some commonly deployed systems use multipart/form-data with file
names directly encoded including octets outside the US-ASCII range.
The encoding used for the file names is typically UTF-8, although
HTML forms will use the charset associated with the form.

Which sounds to me that any charset is valid, regardless of what the other RFC says.

charset is required, AFAICT, only language is optional.

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So, do you think we do not need to check the charset and we should allow anything? Or restrict the charset content only to alnum chars (+ -)?

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IMO, the charset should be restricted to the ABNF from the RFC.

p++;
}
if (*p != '\'') {
msr->mpd->flag_invalid_quoting = 1;
return -17; // Single quote for end-of-language not found
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Shouldn't you use something like this here, as below?

msr->mpd->flag_invalid_quoting = 1;

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It's a good idea - thanks.

@fzipi, @marcstern - what do you think about this guys?

I already added this in 2b22261, but I can remove that.

If we keep this feature, we should add that to v3 too.

}
p++;

/* Now read what should be the actual filename */
const char* start_of_filename = p;
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while ((*p != '\0') && (*p != ';')) {
if (*p == '%') {
if ((*(p+1) == '\0') || (!isxdigit(*(p+1))) || (!isxdigit(*(p+2)))) {
return -18;
}
p += 3;
} else if (isalnum(*p) || strchr(attr_char_special, *p)) {
p++;
} else {
return -19;
}
}
value = apr_pmemdup(msr->mp, start_of_filename, p - start_of_filename);
} else if ((*p == '"') || (*p == '\'')) {
/* quoted */
quote = *p; // remember which quote character was used for the value

Expand Down Expand Up @@ -205,8 +244,7 @@ static int multipart_parse_content_disposition(modsec_rec *msr, char *c_d_value)
log_escape_nq(msr->mp, value));
}
}
else
if (strcmp(name, "filename") == 0) {
else if (strcmp(name, "filename") == 0) {

validate_quotes(msr, value, quote);

Expand All @@ -223,6 +261,17 @@ static int multipart_parse_content_disposition(modsec_rec *msr, char *c_d_value)
msr_log(msr, 9, "Multipart: Content-Disposition filename: %s",
log_escape_nq(msr->mp, value));
}
} else if (strcmp(name, "filename*") == 0) {
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if (filenameStar != NULL && strlen(filenameStar) != 0) {
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msr_log(msr, 4,
"Multipart: Warning: Duplicate Content-Disposition filename*: %s.", log_escape_nq(msr->mp, value));
return -20;
}
filenameStar = apr_pstrdup(msr->mp, value);
if (msr->txcfg->debuglog_level >= 9) {
msr_log(msr, 9, "Multipart: Content-Disposition filename*: %s.",
log_escape_nq(msr->mp, value));
}
}
else return -11;

Expand Down
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