A negative test that I run executes successfully on libxslt-1.0.23, but 
starting in libxslt-1.0.24 it gets a seg fault on line 155 of functions.c.

Here is a reproduction using libxslt-1.0.25.

cd to libxslt-1.0.25/tests/documents/

Here is test.xml:

   <?xml version="1.0"?>
   <files>
   <file name="docfile.xml"/>
   <file name="doc%5Ffile.xml"/>
   </files>

Copy that file to test-bad.xml and modify it so that it references a
a file that does not exist:

   <?xml version="1.0"?>
   <files>
   <file name="foofile.xml"/>
   <file name="foo%5Ffile.xml"/>
   </files>

The output below shows the expected good libxslt-1.0.23 output:

   [jta@gertie documents]$ xsltproc -V
   Using libxml 20430, libxslt 10023 and libexslt 714
   xsltproc was compiled against libxml 20430, libxslt 10023 and libexslt 714
   libxslt 10023 was compiled against libxml 20430
   libexslt 714 was compiled against libxml 20430

   [jta@gertie documents]$ xsltproc test.xsl test.xml

   It work's
   It work's

   [jta@gertie documents]$ xsltproc test.xsl test-bad.xml
   warning: failed to load external entity "foofile.xml"
   warning: failed to load external entity "foo_file.xml"

   Can't Open File: foofile.xml
   Can't Open File: foo%5Ffile.xml

Here is the libxslt-1.0.25 seg fault:

   [jta@gertie documents]$ xsltproc -V
   Using libxml 20502, libxslt 10025 and libexslt 716
   xsltproc was compiled against libxml 20502, libxslt 10025 and libexslt 716
   libxslt 10025 was compiled against libxml 20502
   libexslt 716 was compiled against libxml 20502

   [jta@gertie xsltproc]$ xsltproc test.xsl test-bad.xml
   warning: failed to load external entity "foofile.xml"
   Segmentation fault

It fails on line 155 of functions.c:


   Program received signal SIGSEGV, Segmentation fault.
   xsltDocumentFunctionLoadDocument (ctxt=0x80880b8, URI=0x8088448
"#oofile.xml")
       at functions.c:155
   155      doc = xsltdoc->doc;

There is a problem with processing the block of code below:

    if (xsltdoc == NULL) {                  /* functions.c line 141 */
        if ((URI == NULL) ||
            (URI[0] = '#') ||
            (xmlStrEqual(tctxt->style->doc->URL, URI))) {
            doc = tctxt->style->doc;
        } else {
            valuePush(ctxt, xmlXPathNewNodeSet(NULL));

            if (fragment != NULL)
                xmlFree(fragment);

            return;
        }
    }
    doc = xsltdoc->doc;                    /* functions.c line 155 */


On line 141, the xsltdoc pointer is NULL:

   (gdb) next
   141      if (xsltdoc == NULL) {
   (gdb) print xsltdoc
   $1 = 0x0

And it is still NULL for the assignment on line 155:

   (gdb) next
   155	    doc = xsltdoc->doc;
   (gdb) print xsltdoc
   $1 = 0x0
   (gdb) next

   Program received signal SIGSEGV, Segmentation fault.
   xsltDocumentFunctionLoadDocument (ctxt=0x80880b8, URI=0x8088448   
"#oofile.xml")
       at functions.c:155
   155	    doc = xsltdoc->doc;