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DCSLIB : @(#)Mordred Labs advisory - Remote DoS in PostgreSQL <= 7.2.2



//@(#) Mordred Labs advisory 0x0007

Release date: August 26, 2002
Name: Remote DoS condition in PostgreSQL
Versions affected: <= 7.2.2
Conditions: entry in a pg_hba.conf file that matches attacker's host.
Risk: average
Author: Sir Mordred (http://mslabs.iwebland.com)

I. Description:

PostgreSQL is an advanced object-relational database management system
that supports an extended subset of the SQL standard, including
transactions,
foreign keys, subqueries, triggers, user-defined types and functions.
Check http://www.postgresql.org for more information.


Upon connecting to a database, postmaster will fork a new process.
After that, a child process will call a
src/backend/postmaster/postmaster.c:DoBackend() routine,
which after processing a startup packet (see src/include/libpq/pqcomm.h),
will invoke a src/backend/libpq/auth.c:ClientAuthentication() routine to
perform client authentication.
If there is an entry in pg_hba.conf file, that matches an attacker's host,
an attacker could trigger
invocation of src/backend/libpq/auth.c:recv_and_check_password0(), which
fails to detect a DoS condition.

II. Details:
Consider this snip of code from src/backend/libpq/auth.c:

[snip]
static int recv_and_check_password0(Port *port) {
	int32 len;
	char *buf;

	if (pq_getint(&len, 4) == EOF)
		return STATUS_EOF;
	len -= 4;
	buf = palloc(len); /* len is taken from a packet */
[snip]

Note, that the size of palloced memory is taken from the user's input.


III. How to reproduce:

It's clear from the advisory how to reproduce this.

IV. Solution

Disable network access for untrusted users.