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v2: surface libxml2's parse error in REQBODY_ERROR_MSG and silence its stderr output #3681

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v2: surface libxml2's parse error in REQBODY_ERROR_MSG and silence its stderr output #3681

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25017dc
feat: surface libxml2's parse error in REQBODY_ERROR_MSG
fzipi Oct 13, 2026
f6d6d5e
fix: set XML_PARSE_NOERROR on the XML body parser contexts
fzipi Oct 13, 2026
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64 changes: 49 additions & 15 deletions apache2/msc_xml.c
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,9 @@

#include "msc_xml.h"

#include <ctype.h>
#include <string.h>

static void msc_xml_on_start_elementns(
void *ctx,
const xmlChar *localname,
Expand Down Expand Up @@ -200,21 +203,44 @@ int xml_init(modsec_rec *msr, char **error_msg) {
return 1;
}

#if 0
static void xml_receive_sax_error(void *data, const char *msg, ...) {
modsec_rec *msr = (modsec_rec *)data;
char message[256];
/**
* Build the error message from libxml2's last error on the context, so the
* actual reason ("Extra content at the end of the document", a tag mismatch,
* ...) reaches REQBODY_ERROR_MSG and the logs instead of a fixed string.
* Falls back to "XML: <what>." when libxml2 has no message.
* xmlCtxtGetLastError() keeps working under XML_PARSE_NOERROR.
*/
static char *xml_parse_error(modsec_rec *msr, xmlParserCtxtPtr ctx, const char *what) {
const xmlError *e = (ctx != NULL) ? xmlCtxtGetLastError(ctx) : NULL;
char *detail;
size_t len;

if (msr == NULL) return;
assert(msr != NULL);
assert(what != NULL);

apr_snprintf(message, sizeof(message), "%s (line %d offset %d)",
log_escape_nq(msr->mp, msr->xml->parsing_ctx->lastError.message),
msr->xml->parsing_ctx->lastError.line,
msr->xml->parsing_ctx->lastError.int2);
if (e == NULL || e->message == NULL || e->message[0] == '\0') {
return apr_psprintf(msr->mp, "XML: %s.", what);
}

detail = apr_pstrdup(msr->mp, e->message);
len = strlen(detail);
while (len > 0 && isspace((unsigned char)detail[len - 1])) {
detail[--len] = '\0';
}

msr_log(msr, 5, "XML: Parsing error: %s", message);
return apr_psprintf(msr->mp, "XML: %s: %s (line %d, column %d)",
what, log_escape_nq(msr->mp, detail), e->line, e->int2);
}

/**
* Keep libxml2 from writing parser errors to stderr on its own; the reason
* is reported through xml_parse_error() instead. Must go through
* xmlCtxtUseOptions(): OR-ing ctx->options directly is a no-op before
* libxml2 2.13 (see v3 #3563).
*/
static void xml_silence_parser(xmlParserCtxtPtr ctx) {
xmlCtxtUseOptions(ctx, XML_PARSE_NOWARNING | XML_PARSE_NOERROR);
}
#endif

/**
* Feed one chunk of data to the XML parser.
Expand Down Expand Up @@ -252,6 +278,7 @@ int xml_process_chunk(modsec_rec *msr, const char *buf, unsigned int size, char
*error_msg = apr_psprintf(msr->mp, "XML: Failed to create parsing context.");
return -1;
}
xml_silence_parser(msr->xml->parsing_ctx);
}
if (msr->txcfg->parse_xml_into_args != MSC_XML_ARGS_OFF) {
msr->xml->parsing_ctx_arg = xmlCreatePushParserCtxt(
Expand All @@ -264,6 +291,7 @@ int xml_process_chunk(modsec_rec *msr, const char *buf, unsigned int size, char
*error_msg = apr_psprintf(msr->mp, "XML: Failed to create parsing context for ARGS.");
return -1;
}
xml_silence_parser(msr->xml->parsing_ctx_arg);
}
} else {

Expand All @@ -273,7 +301,8 @@ int xml_process_chunk(modsec_rec *msr, const char *buf, unsigned int size, char
msr->txcfg->parse_xml_into_args != MSC_XML_ARGS_ONLYARGS) {
xmlParseChunk(msr->xml->parsing_ctx, buf, size, 0);
if (msr->xml->parsing_ctx->wellFormed != 1) {
*error_msg = apr_psprintf(msr->mp, "XML: Failed to parse document.");
*error_msg = xml_parse_error(msr, msr->xml->parsing_ctx,
"Failed to parse document");
return -1;
}
}
Expand All @@ -285,7 +314,8 @@ int xml_process_chunk(modsec_rec *msr, const char *buf, unsigned int size, char
*error_msg = msr->xml->xml_error;
}
else {
*error_msg = apr_psprintf(msr->mp, "XML: Failed to parse document for ARGS.");
*error_msg = xml_parse_error(msr, msr->xml->parsing_ctx_arg,
"Failed to parse document for ARGS");
}
return -1;
}
Expand Down Expand Up @@ -317,14 +347,17 @@ int xml_complete(modsec_rec *msr, char **error_msg) {
/* Preserve the results for our reference. */
msr->xml->well_formed = msr->xml->parsing_ctx->wellFormed;
msr->xml->doc = msr->xml->parsing_ctx->myDoc;
if (msr->xml->well_formed != 1) {
*error_msg = xml_parse_error(msr, msr->xml->parsing_ctx,
"Failed to parse document");
}

/* Clean up everything else. */
xmlFreeParserCtxt(msr->xml->parsing_ctx);
msr->xml->parsing_ctx = NULL;
msr_log(msr, 4, "XML: Parsing complete (well_formed %u).", msr->xml->well_formed);

if (msr->xml->well_formed != 1) {
*error_msg = apr_psprintf(msr->mp, "XML: Failed to parse document.");
return -1;
}
}
Expand All @@ -336,7 +369,8 @@ int xml_complete(modsec_rec *msr, char **error_msg) {
*error_msg = msr->xml->xml_error;
}
else {
*error_msg = apr_psprintf(msr->mp, "XML: Failed to parse document for ARGS.");
*error_msg = xml_parse_error(msr, msr->xml->parsing_ctx_arg,
"Failed to parse document for ARGS");
}
xmlFreeParserCtxt(msr->xml->parsing_ctx_arg);
msr->xml->parsing_ctx_arg = NULL;
Expand Down
73 changes: 73 additions & 0 deletions tests/regression/target/10-variable-reqbody_error_msg-xml.t
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Original file line number Diff line number Diff line change
@@ -0,0 +1,73 @@
### REQBODY_ERROR_MSG for XML parse failures (#3680)
#
# libxml2's own reason (with line and column) must reach the error message.
# The parser contexts also carry XML_PARSE_NOERROR, so libxml2's own
# "body.xml:N: parser error" lines must never show up in the error log
# (Apache's stderr); the -error checks below guard that.

# Tag mismatch
{
type => "target",
comment => "REQBODY_ERROR_MSG carries the libxml2 reason (tag mismatch)",
conf => qq(
SecRuleEngine On
SecRequestBodyAccess On
SecDebugLog $ENV{DEBUG_LOG}
SecDebugLogLevel 9
SecRule REQUEST_HEADERS:Content-Type "^text/xml\$" "id:500005, \\
phase:1,t:none,t:lowercase,nolog,pass,ctl:requestBodyProcessor=XML"
),
match_log => {
error => [ qr/XML parser error: XML: Failed to parse document: Opening and ending tag mismatch: book line \d+ and bookasdf \(line \d+, column \d+\)/, 1 ],
-error => [ qr/body\.xml:\d+: parser error/, 1 ],
debug => [ qr/XML: Parsing complete \(well_formed 0\)/, 1 ],
},
match_response => {
status => qr/^500$/,
},
request => new HTTP::Request(
POST => "http://$ENV{SERVER_NAME}:$ENV{SERVER_PORT}/test.txt",
[
"Content-Type" => "text/xml",
],
normalize_raw_request_data(
q(
<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
<book category="WEB">
<title lang="en">Learning XML</title>
<author>Erik T. Ray</author>
</bookasdf>
</bookstore>
),
),
),
},

# Extra content after the root element (the #3563 reproducer)
{
type => "target",
comment => "REQBODY_ERROR_MSG carries the libxml2 reason (extra content)",
conf => qq(
SecRuleEngine On
SecRequestBodyAccess On
SecDebugLog $ENV{DEBUG_LOG}
SecDebugLogLevel 9
SecRule REQUEST_HEADERS:Content-Type "^text/xml\$" "id:500005, \\
phase:1,t:none,t:lowercase,nolog,pass,ctl:requestBodyProcessor=XML"
),
match_log => {
error => [ qr/XML parser error: XML: Failed to parse document: Extra content at the end of the document \(line \d+, column \d+\)/, 1 ],
-error => [ qr/body\.xml:\d+: parser error/, 1 ],
},
match_response => {
status => qr/^500$/,
},
request => new HTTP::Request(
POST => "http://$ENV{SERVER_NAME}:$ENV{SERVER_PORT}/test.txt",
[
"Content-Type" => "text/xml",
],
"<xml></xml> Testing modsec",
),
},
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