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CVE-2015-7547 MegaBug wating to hit electronic devices

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TechGlyphs Editor

A highly critical vulnerability has been uncovered in the GNU C Library (glibc), a key component of most Linux distributions, that leaves nearly all Linux machines, thousands of apps and electronic devices vulnerable to hackers.


GNU C Library (glibc) is a collection of open source code that powers thousands of standalone apps and most Linux distributions, including those distributed to routers and other types of hardware.The flaw can be exploited when an affected device or app make queries to a malicious DNS server that returns too much information to a lookup request and floods the program's memory with code.


This code then compromises the vulnerable application or device and tries to take over the control over the whole system.


It is possible to inject the domain name into server log files, which when resolved will trigger remote code execution. An SSH (Secure Shell) client connecting to a server could also be compromised.


However, an attacker need to bypass several operating system security mechanisms – like ASLR and non-executable stack protection – in order to achieve successful RCE attack.


Alternatively, an attacker on your network could perform man-in-the-middle (MitM) attacks and tamper with DNS replies in a view to monitoring and manipulating (injecting payloads of malicious code) data flowing between a vulnerable device and the Internet."glibc reserves 2048 bytes in the stack through alloca() for the DNS answer at _nss_dns_gethostbyname4_r() for hosting responses to a DNS query. Later on, at send_dg() and send_vc(), if the response is larger than 2048 bytes, a new buffer is allocated from the heap and all the information (buffer pointer, new buffer size and response size) is updated."

"Under certain conditions a mismatch between the stack buffer and the new heap allocation will happen. The final effect is that the stack buffer will be used to store the DNS response, even though the response is larger than the stack buffer and a heap buffer was allocated. This behavior leads to the stack buffer overflow."


you can help prevent exploitation of the flaw, if you aren’t able to immediately patch your instance of glibc, by limiting all TCP DNS replies to 1024 bytes, and dropping UDP DNS packets larger than 512 bytes



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