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<base href="https://bugs.freedesktop.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Off by one reading out of bound in _jpeg_skip_segment"
href="https://bugs.freedesktop.org/show_bug.cgi?id=101427">101427</a>
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<th>Summary</th>
<td>Off by one reading out of bound in _jpeg_skip_segment
</td>
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<th>Product</th>
<td>cairo
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>image backend
</td>
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<th>Assignee</th>
<td>chris@chris-wilson.co.uk
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<th>Reporter</th>
<td>foca@salesforce.com
</td>
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<th>QA Contact</th>
<td>cairo-bugs@cairographics.org
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<p>
<div>
<pre>There is an off by one vulnerability in cairo, reading the jpeg headers of an
image surface.
The vulnerability is at cairo-image-info.c:76:
70 static const unsigned char *
71 _jpeg_skip_segment (const unsigned char *p)
72 {
73 int len;
74
75 p++;
76 len = (p[0] << 8) | p[1];
77
78 return p + len;
79 }
The off by one happens while reading the variable p[1].
This function is called from line cairo-image-info.c:143:
139
140 if (p + 2 > data + length)
141 return CAIRO_INT_STATUS_UNSUPPORTED;
142
143 p = _jpeg_skip_segment (p);
144 break;
145 }
The check here should be >= instead of >:
140 if (p + 2 >= data + length)
Since in _jpeg_skip_segment 3 bytes are consumed (1 skipped and 2 read).
If an attacker could control p[1] then he could control how many bytes are
skipped reading the jpeg segment. It doesn't look this vulnerability has
security implications since the function _cairo_image_info_get_jpeg_info is
validating that the pointer is inside the bounds.</pre>
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