AUSCERT External Security Bulletin Redistribution

                ESB-2003.0540 -- OpenBSD Security Advisory
                      off-by-one error in realpath(3)
                              05 August 2003


        AusCERT Security Bulletin Summary

Product:                libc function: realpath(3)
Publisher:              OpenBSD
Operating System:       OpenBSD 3.3 and prior
Impact:                 Denial of Service
                        Execute Arbitrary Code/Commands
                        Increased Privileges

Ref:                    AL-2003.13

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An off-by-one error exists in the C library function realpath(3).
This is the same bug that was recently found in the wu-ftpd ftpd
server by Janusz Niewiadomski and Janusz Niewiadomski.

The OpenBSD ftp daemon does not use realpath(3) in a way that could
be exploited, however a number of other system binaries also use
the function.  It is not currently known whether or not this bug
results in an exploitable security hole on OpenBSD.  Since the bug
led to an exploitable hole in wu-ftpd, it is entirely possible that
some program using realpath(3) under OpenBSD may be vulnerable to
attack.  For OpenBSD 3.3 and higher, the ProPolice stack protector
should provide some protection from this bug, but this cannot be

This bug has been fixed in OpenBSD-current as well as the 3.2 and
3.3 stable branches.  Patches are available for OpenBSD 3.2 and 3.3.

Patch for OpenBSD 3.2:

Patch for OpenBSD 3.3:

For versions of OpenBSD prior to 3.2, users may simply fetch
the current revision of realpath.c from:
then rebuild and install libc with the new realpath.c.

For more details, see the description of the wu-ftpd fp_realpath bug:

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