@(#)Mordred Labs advisory 0x0007: Remove DoS in PostgreSQL

//@(#) Mordred Labs advisory 0x0007

Release data: 26/08/02
Name: Remote DoS condition in PostgreSQL
Versions affected: all versions
Conditions: entry in a pg_hba.conf file that matches attacker's host.
Risk: average

---[ Description:

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.

---[ 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,
which is stupid if you ask me.

--[ How to reproduce:

I dont want to provide any tools to illustrate this vulnerability.

--[ Solution

Disable network access for untrusted users.

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