Buffer overflow protection: Difference between revisions

Revision as of 05:02, 11 November 2021

Revision as of 03:17, 18 January 2022

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Stack buffer overflow can be caused deliberately as part of an attack known as [[stack smashing]]. If the affected program is running with special privileges, or if it accepts data from untrusted network hosts (for example, a public [[webserver]]), then the bug is a potential security vulnerability that allows an [[hacker (computer security)|attacker]] to inject executable code into the running program and take control of the process. This is one of the oldest and more reliable methods for attackers to gain unauthorized access to a computer.<ref>{{cite journal |last=Levy |first=Elias |author-link=Elias Levy |title=Smashing The Stack for Fun and Profit |journal=[[Phrack]] |volume=7 |issue=49 |page=14 |date=1996-11-08 |url=http://www.phrack.org/issues/49/14.html#article }}</ref>

Typically, buffer overflow protection modifies the organization of data in the [[stack frame]] of a [[function call]] to include a "canary" value that, when destroyed, shows that a buffer preceding it in memory has been overflowed. This provides the benefit of preventing an entire class of attacks. According to some researchers,<ref>{{cite web|url=httphttps://tmp-www.cpe.ku.ac.th/~mcs/courses/2005_02/214573/papers/buffer_overflows.pdf |title=Buffer Overflows: Attacks and Defenses for the Vulnerability of the Decade* |url-status=dead |archive-url=https://web.archive.org/web/20130309083252/http://tmp-www.cpe.ku.ac.th/~mcs/courses/2005_02/214573/papers/buffer_overflows.pdf |archive-date=2013-03-09 }}</ref> the performance impact of these techniques is negligible.

Stack-smashing protection is unable to protect against certain forms of attack. For example, it cannot protect against buffer overflows in the heap. There is no sane way to alter the layout of data within a [[Data structure|structure]]; structures are expected to be the same between modules, especially with shared libraries. Any data in a structure after a buffer is impossible to protect with canaries; thus, programmers must be very careful about how they organize their variables and use their structures.