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Date: Tue, 09 Apr 2024 15:03:54 +0000
From: Michael Knap <oss-sec@...ap.com>
To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: CWE-121, CWE-122: libfreeimage 3.40-3.18/19+ buffer overflow
Hello,
I have identified two buffer overflow vulnerabilities in
libfreeimage -> PluginXPM.cpp module, Load function.
Issue reported on 2024-03-28 but not acknowledged by maintainer yet:
https://sourceforge.net/p/freeimage/bugs/355/
CWE-121: Stack-based Buffer Overflow
CWE-122: Heap-based Buffer Overflow (consequence of the first bug)
Technical Details:
The vulnerability is present in the code responsible for parsing color
names from XPM files. Specifically, the buffer char msg[256];
is susceptible to overflow in Load function:
static FIBITMAP * DLL_CALLCONV
Load(FreeImageIO *io, fi_handle handle, int page, int flags, void *data) {
char msg[256]; // This is overflown.
FIBITMAP *dib = NULL;
...// redacted for brevity
if (!FreeImage_LookupX11Color(clr, &rgba.r, &rgba.g, &rgba.b)) {
// Arbitrary length buffer write.
sprintf(msg, "Unknown color name '%s'", str);
free(str);
throw msg;
}
...// redacted for brevity
return dib;
} catch(const char *text) {
// 512-byte buffer allocated on the heap in following function.
FreeImage_OutputMessageProc(s_format_id, text);
if( dib != NULL )
FreeImage_Unload(dib);
return NULL;
}
}
A doctored XPM file ("trigger.xpm" attached) with an excessively
long color name can trigger this buffer overflow. Moreover, when msg is thrown
and passed to FreeImage_OutputMessageProc (FreeImage.cpp), there exists another critical
vulnerability:
This function handles the error message with a dynamically allocated 512-byte buffer,
which could also overflow if the error message is too long.
The latter depends on accurately overflown free argument which would lead to
freeing arbitrary memory and subsequently lead to Heap Buffer Overflow when
the msg is thrown and written to a message buffer in FreeImage_OutputMessageProc.
void DLL_CALLCONV
FreeImage_OutputMessageProc(int fif, const char *fmt, ...) {
// Developer assumes the message is short (my comment).
const int MSG_SIZE = 512; // 512 bytes should be more than enough for a short message
// redacted for brevity...
int str_length = (int)( (strlen(fmt) > MSG_SIZE) ? MSG_SIZE : strlen(fmt) );
// redacted for brevity...
for (int i = 0, j = 0; i < str_length; ++i) {
if (fmt[i] == '%') {
if (i + 1 < str_length) {
switch(tolower(fmt[i + 1])) {
case '%' :
message[j++] = '%';
break;
case 'o' : // octal numbers
{
char tmp[16];
_itoa(va_arg(arg, int), tmp, 8);
strcat(message, tmp);
j += (int)strlen(tmp);
++i;
break;
}
// other cases redacted for brevity...
};
} else {
message[j++] = fmt[i];
}} else {
message[j++] = fmt[i];
};
}
// redacted for brevity...
}
strcat is used to write to message buffer without validating if the message content
exceeds the buffer length.
Impact Analysis:
This vulnerability could allow an attacker to execute arbitrary code or
cause a Denial of Service (DoS) by crashing the application.
Suggested Mitigations:
To address this vulnerability, developers are encouraged to undertake following actions:
- Implement proper bounds checking for all input data, particularly for strings
derived from file content or user input, to prevent overflow.
- Replace sprintf with safer string handling functions that enforce buffer size limits,
such as snprintf, or consider using higher-level string processing mechanisms provided
by modern C++ standards, which inherently manage memory more safely.
Best Regards,
Michael Knap
Download attachment "trigger.xpm" of type "image/x-xpixmap" (634 bytes)
Download attachment "publickey - oss-sec@...ap.com - 0xDF4CFAF0.asc" of type "application/pgp-keys" (641 bytes)
Download attachment "signature.asc" of type "application/pgp-signature" (250 bytes)
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