Harden three parser buffer copies against overflow

Width-less sscanf("%s %s %s") parsed a request line into fixed method/url/
protocol buffers in the catch-URL proxy (htscatchurl.c) and the postfile
sender (htslib.c), so a long token could overflow the smallest one
(method[32] / [256]). Add field widths matching each buffer.

The makeindex title decoder copied the UTF-8-expanded title into s[] with a
raw strcpy; a charset that expands past the buffer would overflow it.
Truncate with snprintf and free through freet.

The entity/URL unescapers guarded the copy with `j + 1 > max`, which reserves
nothing for the trailing NUL: an input filling dest to exactly `max` chars
wrote dest[max], one byte past a max-sized buffer. Every production caller
passes max = buffer capacity (strlen+1 or sizeof), so this was a real 1-byte
OOB, latent only because output is usually shorter than the buffer. Use
`>=`. The st_entities self-test passed max = strlen (relying on strdup's
extra byte); correct it to strlen+1 to match the callers.

Self-test unescape-bounds exercises the exact-fill boundary on both
unescapers; it aborts under ASan on the pre-fix guard.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Xavier Roche <roche@httrack.com>

src/htscatchurl.c

@@ -175,7 +175,9 @@ HTSEXT_API hts_boolean catch_url(T_SOC soc, char *url, char *method,
       //
       socinput(soc, line, 1000);
       if (strnotempty(line)) {
-        if (sscanf(line, "%s %s %s", method, url, protocol) == 3) {
+        /* widths bound the caller buffers: method[32], url[HTS_URLMAXSIZE*2],
+           protocol[256] */
+        if (sscanf(line, "%31s %2047s %255s", method, url, protocol) == 3) {
           lien_adrfil af;
 
           // méthode en majuscule

src/htsencoding.c

@@ -190,9 +190,9 @@ int hts_unescapeEntitiesWithCharset(const char *src, char *dest, const size_t ma
         }
       }
     }
-    
-    /* copy */
-    if (j + 1 > max) {
+
+    /* reserve one byte for the trailing NUL written after the loop */
+    if (j + 1 >= max) {
       /* overflow */
       return -1;
     }
@@ -314,8 +314,8 @@ int hts_unescapeUrlSpecial(const char *src, char *dest, const size_t max,
       }
     }
 
-    /* Check for overflow */
-    if (j + 1 > max) {
+    /* reserve one byte for the trailing NUL written after the loop */
+    if (j + 1 >= max) {
       return -1;
     }
 

src/htslib.c

@@ -1149,7 +1149,8 @@ int http_sendhead(httrackp * opt, t_cookie * cookie, int mode,
           char BIGSTK protocol[256], url[HTS_URLMAXSIZE * 2], method[256];
 
           linput(fp, line, 1000);
-          if (sscanf(line, "%s %s %s", method, url, protocol) == 3) {
+          /* widths bound method[256], url[HTS_URLMAXSIZE*2], protocol[256] */
+          if (sscanf(line, "%255s %2047s %255s", method, url, protocol) == 3) {
             size_t ret;
             // selon que l'on a ou pas un proxy
             if (retour->req.proxy.active) {

src/htsparse.c

@@ -604,13 +604,14 @@ int htsparse(htsmoduleStruct * str, htsmoduleStructExtended * stre) {
                         }
 
                         // Decode title with encoding
-                        if (str->page_charset_ != NULL 
-                            && *str->page_charset_ != '\0') {
-                          char *const sUtf = 
-                            hts_convertStringToUTF8(s, strlen(s), str->page_charset_);
+                        if (str->page_charset_ != NULL &&
+                            *str->page_charset_ != '\0') {
+                          char *sUtf = hts_convertStringToUTF8(
+                              s, strlen(s), str->page_charset_);
                           if (sUtf != NULL) {
-                            strcpy(s, sUtf);
-                            free(sUtf);
+                            /* UTF-8 can expand past s[]; truncate to fit */
+                            snprintf(s, sizeof(s), "%s", sUtf);
+                            freet(sUtf);
                           }
                         }
 

src/htsselftest.c

@@ -708,7 +708,8 @@ static int st_entities(httrackp *opt, int argc, char **argv) {
   }
   s = strdupt(argv[0]);
   enc = argc >= 2 ? argv[1] : "UTF-8";
-  if (s != NULL && hts_unescapeEntitiesWithCharset(s, s, strlen(s), enc) == 0) {
+  if (s != NULL &&
+      hts_unescapeEntitiesWithCharset(s, s, strlen(s) + 1, enc) == 0) {
     printf("%s\n", s);
     freet(s);
   } else {
@@ -717,6 +718,23 @@ static int st_entities(httrackp *opt, int argc, char **argv) {
   return 0;
 }
 
+/* The unescapers must reserve one byte for the trailing NUL: a 'max'-byte
+   dest holding 'max' output chars pre-fix wrote dest[max] (1-byte OOB, caught
+   by ASan). Both unescapeEntities and unescapeUrl share the guard. */
+static int st_unescape_bounds(httrackp *opt, int argc, char **argv) {
+  char dest[4];
+
+  (void) opt;
+  (void) argc;
+  (void) argv;
+  assertf(hts_unescapeEntities("abcd", dest, sizeof(dest)) == -1);
+  assertf(hts_unescapeUrl("abcd", dest, sizeof(dest)) == -1);
+  assertf(hts_unescapeEntities("abc", dest, sizeof(dest)) == 0);
+  assertf(strcmp(dest, "abc") == 0);
+  printf("unescape-bounds self-test OK\n");
+  return 0;
+}
+
 static int st_hashtable(httrackp *opt, int argc, char **argv) {
   char *snum;
   unsigned long count = 0;
@@ -1799,6 +1817,8 @@ static const struct selftest_entry {
     {"idna-decode", "<host>", "decode an IDNA/punycode hostname",
      st_idna_decode},
     {"entities", "<string> [encoding]", "unescape HTML entities", st_entities},
+    {"unescape-bounds", "", "unescapers reserve the NUL byte (no 1-byte OOB)",
+     st_unescape_bounds},
     {"hashtable", "<count|file>", "coucal hashtable stress test", st_hashtable},
     {"strsafe", "[overflow|overflow-buff [str]]", "bounded string-op self-test",
      st_strsafe},

tests/01_engine-unescape-bounds.test

@@ -0,0 +1,7 @@
+#!/bin/bash
+#
+
+set -euo pipefail
+
+# Entity/URL unescapers reserve one byte for the trailing NUL (no 1-byte OOB).
+httrack -O /dev/null -#test=unescape-bounds run | grep -q "unescape-bounds self-test OK"

tests/Makefile.am

@@ -54,6 +54,7 @@ TESTS = \
 	01_engine-stripquery.test \
 	01_engine-strsafe.test \
 	01_engine-urlhack.test \
+	01_engine-unescape-bounds.test \
 	01_engine-useragent.test \
 	01_zlib-acceptencoding.test \
 	01_zlib-cache.test \