An integer overflow during the parsing of XML using the Expat library.
The CGIHTTPServer module in Python 2.7.5 and 3.3.4 does not properly handle URLs in which URL encoding is used for path separators, which allows remote attackers to read script source code or conduct directory traversal attacks and execute unintended code via a crafted character sequence, as demonstrated by a %2f separator.
It was found that original patch for issues CVE-2015-1283 and CVE-2015-2716 used overflow checks that could be optimized out by some compilers applying certain optimization settings, which can cause the vulnerability to remain even after applying the patch.
One pattern in the fix for CVE-2015-1283/CVE-2015-2716 is:
/ bufferSize is positive here / do { bufferSize = 2; } while (bufferSize < neededSize && bufferSize > 0); if (bufferSize <= 0) { errorCode = XMLERRORNOMEMORY; return NULL;
Any of the modern optimizing compiler, IF able to infer that bufferSize is initially positive (which is true but not obvious to see through local reasoning), will eliminate bufferSize > 0 as always true when the execution is defined, and bufferSize <= 0 as always false when the execution is defined.
Without knowing that bufferSize starts positive, an optimizing compiler could also move the test bufferSize > 0 out of the loop, that is, compile the code as if it had been written:
if (bufferSize <= 0) errorCode = XMLERRORNOMEMORY; return NULL; else { do { bufferSize = 2; } while (bufferSize < neededSize); }
Both cases leads to not eliminating the vulnerability.
Upstream patch:
https://sourceforge.net/p/expat/codegit/ci/f0bec73b018caa07d3e75ec8dd967f3785d71bde/tree/expat/lib/xmlparse.c?diff=a238d7ea7a715ef3850c4cbdd86aeda7077b6bbc
The gzipdecode function in the xmlrpc client library in Python 3.4 and earlier allows remote attackers to cause a denial of service (memory consumption) via a crafted HTTP request.
Last updated 24 July 2024
Dominic Scheirlinck of VendHQ reports:
Many software projects and vendors have implemented support for the “Proxy” request header in their respective CGI implementations and languages by creating the “HTTPPROXY” environmental variable based on the header value. When this variable is used (in many cases automatically by various HTTP client libraries) any outgoing requests generated in turn from the attackers original request can be redirected to an attacker controlled proxy. This allows attackers to view potentially sensitive information, reply with malformed data, or to hold connections open causing a potential denial of service.
Last updated 24 July 2024