pdfresurrect 0.15 - Buffer Overflow

EDB-ID:

47178


Author:

j0lama

Type:

dos


Platform:

Linux

Date:

2019-07-26


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# Exploit Title: pdfresurrect 0.15 Buffer Overflow
# Date: 2019-07-26
# Exploit Author: j0lama
# Vendor Homepage: https://github.com/enferex/pdfresurrect
# Software Link: https://github.com/enferex/pdfresurrect
# Version: 0.15
# Tested on: Ubuntu 18.04
# CVE : CVE-2019-14267

Description
===========

PDFResurrect 0.15 has a buffer overflow via a crafted PDF file because
data associated with startxref and %%EOF is mishandled.


Additional Information
======================

There is a buffer overflow in pdfresurrect 0.14 caused by a malicious
 crafted pdf file.

In function pdf_load_xrefs at pdf.c file, it counts how many times the
strings '%%EOF' appear in the pdf file. Then for each xref the code
starts to rewind incrementing the pos_count variable until found a 'f'
character (the last character of the 'startxref' string). Then these
bytes between the 'f' and '%%EOF' will be read with the 'fread'
function and copied to a 256 char buffer. The 'pos_count' variable
tells 'freads' how many bytes has to copy. If malicious user crafted a
pdf file with more that 256 bytes between '%%EOF' and the immediately
previous 'f' then a buffer overflow will occur overwriting everything
after the 'buf' buffer.

In the code:
int pdf_load_xrefs(FILE *fp, pdf_t *pdf)
{
    int  i, ver, is_linear;
    long pos, pos_count;
    char x, *c, buf[256];

    c = NULL;

    /* Count number of xrefs */
    pdf->n_xrefs = 0;
    fseek(fp, 0, SEEK_SET);
    while (get_next_eof(fp) >= 0)
      ++pdf->n_xrefs;

    if (!pdf->n_xrefs)
      return 0;

    /* Load in the start/end positions */
    fseek(fp, 0, SEEK_SET);
    pdf->xrefs = calloc(1, sizeof(xref_t) * pdf->n_xrefs);
    ver = 1;
    for (i=0; i<pdf->n_xrefs; i++)
    {
        /* Seek to %%EOF */
        if ((pos = get_next_eof(fp)) < 0)
          break;

        /* Set and increment the version */
        pdf->xrefs[i].version = ver++;

        /* Rewind until we find end of "startxref" */
        pos_count = 0;
        while (SAFE_F(fp, ((x = fgetc(fp)) != 'f'))) <== The loop will continue incrementing pos_count until find a 'f' char
          fseek(fp, pos - (++pos_count), SEEK_SET);

        /* Suck in end of "startxref" to start of %%EOF */
        memset(buf, 0, sizeof(buf));
        SAFE_E(fread(buf, 1, pos_count, fp), pos_count, <== If pos_count > 256 then a buffer overflow occur
               "Failed to read startxref.\n");
        c = buf;
        while (*c == ' ' || *c == '\n' || *c == '\r')
          ++c;

        /* xref start position */
        pdf->xrefs[i].start = atol(c);

This is a crafted PDF that produces a buffer overflow: 

http://www.mediafire.com/file/3540cyrl7o8p1rq/example_error.pdf/file
https://github.com/offensive-security/exploitdb-bin-sploits/raw/master/bin-sploits/47178.zip