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author | Tom Lane <tgl@sss.pgh.pa.us> | 2021-11-08 11:14:56 -0500 |
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committer | Tom Lane <tgl@sss.pgh.pa.us> | 2021-11-08 11:14:56 -0500 |
commit | 160c0258802d10b0600d7671b1bbea55d8e17d45 (patch) | |
tree | 03497de0aa9ef32205ce20c731fb92c986c019df /src/interfaces/libpq/fe-connect.c | |
parent | 28e24125541545483093819efae9bca603441951 (diff) | |
download | postgresql-160c0258802d10b0600d7671b1bbea55d8e17d45.tar.gz |
libpq: reject extraneous data after SSL or GSS encryption handshake.
libpq collects up to a bufferload of data whenever it reads data from
the socket. When SSL or GSS encryption is requested during startup,
any additional data received with the server's yes-or-no reply
remained in the buffer, and would be treated as already-decrypted data
once the encryption handshake completed. Thus, a man-in-the-middle
with the ability to inject data into the TCP connection could stuff
some cleartext data into the start of a supposedly encryption-protected
database session.
This could probably be abused to inject faked responses to the
client's first few queries, although other details of libpq's behavior
make that harder than it sounds. A different line of attack is to
exfiltrate the client's password, or other sensitive data that might
be sent early in the session. That has been shown to be possible with
a server vulnerable to CVE-2021-23214.
To fix, throw a protocol-violation error if the internal buffer
is not empty after the encryption handshake.
Our thanks to Jacob Champion for reporting this problem.
Security: CVE-2021-23222
Diffstat (limited to 'src/interfaces/libpq/fe-connect.c')
-rw-r--r-- | src/interfaces/libpq/fe-connect.c | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c index b288d346f9..f0fdd294a4 100644 --- a/src/interfaces/libpq/fe-connect.c +++ b/src/interfaces/libpq/fe-connect.c @@ -3097,6 +3097,19 @@ keep_going: /* We will come back to here until there is pollres = pqsecure_open_client(conn); if (pollres == PGRES_POLLING_OK) { + /* + * At this point we should have no data already buffered. + * If we do, it was received before we performed the SSL + * handshake, so it wasn't encrypted and indeed may have + * been injected by a man-in-the-middle. + */ + if (conn->inCursor != conn->inEnd) + { + appendPQExpBufferStr(&conn->errorMessage, + libpq_gettext("received unencrypted data after SSL response\n")); + goto error_return; + } + /* SSL handshake done, ready to send startup packet */ conn->status = CONNECTION_MADE; return PGRES_POLLING_WRITING; @@ -3196,6 +3209,19 @@ keep_going: /* We will come back to here until there is pollres = pqsecure_open_gss(conn); if (pollres == PGRES_POLLING_OK) { + /* + * At this point we should have no data already buffered. + * If we do, it was received before we performed the GSS + * handshake, so it wasn't encrypted and indeed may have + * been injected by a man-in-the-middle. + */ + if (conn->inCursor != conn->inEnd) + { + appendPQExpBufferStr(&conn->errorMessage, + libpq_gettext("received unencrypted data after GSSAPI encryption response\n")); + goto error_return; + } + /* All set for startup packet */ conn->status = CONNECTION_MADE; return PGRES_POLLING_WRITING; |