From 28e24125541545483093819efae9bca603441951 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 8 Nov 2021 11:01:43 -0500 Subject: [PATCH] Reject extraneous data after SSL or GSS encryption handshake. The server collects up to a bufferload of data whenever it reads data from the client socket. When SSL or GSS encryption is requested during startup, any additional data received with the initial request message 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 be abused to send faked SQL commands to the server, although that would only work if the server did not demand any authentication data. (However, a server relying on SSL certificate authentication might well not do so.) 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-2021-23214 --- src/backend/libpq/pqcomm.c | 12 ++++++++++++ src/backend/postmaster/postmaster.c | 24 ++++++++++++++++++++++++ src/include/libpq/libpq.h | 1 + 3 files changed, 37 insertions(+) diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c index 89a5f901aa..44782f2d88 100644 --- a/src/backend/libpq/pqcomm.c +++ b/src/backend/libpq/pqcomm.c @@ -1141,6 +1141,18 @@ pq_discardbytes(size_t len) return 0; } +/* -------------------------------- + * pq_buffer_has_data - is any buffered data available to read? + * + * This will *not* attempt to read more data. + * -------------------------------- + */ +bool +pq_buffer_has_data(void) +{ + return (PqRecvPointer < PqRecvLength); +} + /* -------------------------------- * pq_startmsgread - begin reading a message from the client. diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c index e2a76ba055..db797c040b 100644 --- a/src/backend/postmaster/postmaster.c +++ b/src/backend/postmaster/postmaster.c @@ -2110,6 +2110,18 @@ retry1: return STATUS_ERROR; #endif + /* + * 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. + * We report this case to the client. + */ + if (pq_buffer_has_data()) + ereport(FATAL, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("received unencrypted data after SSL request"), + errdetail("This could be either a client-software bug or evidence of an attempted man-in-the-middle attack."))); + /* * regular startup packet, cancel, etc packet should follow, but not * another SSL negotiation request, and a GSS request should only @@ -2142,6 +2154,18 @@ retry1: return STATUS_ERROR; #endif + /* + * 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. + * We report this case to the client. + */ + if (pq_buffer_has_data()) + ereport(FATAL, + (errcode(ERRCODE_PROTOCOL_VIOLATION), + errmsg("received unencrypted data after GSSAPI encryption request"), + errdetail("This could be either a client-software bug or evidence of an attempted man-in-the-middle attack."))); + /* * regular startup packet, cancel, etc packet should follow, but not * another GSS negotiation request, and an SSL request should only diff --git a/src/include/libpq/libpq.h b/src/include/libpq/libpq.h index 6c51b2f20f..6b67a2a318 100644 --- a/src/include/libpq/libpq.h +++ b/src/include/libpq/libpq.h @@ -79,6 +79,7 @@ extern int pq_getmessage(StringInfo s, int maxlen); extern int pq_getbyte(void); extern int pq_peekbyte(void); extern int pq_getbyte_if_available(unsigned char *c); +extern bool pq_buffer_has_data(void); extern int pq_putmessage_v2(char msgtype, const char *s, size_t len); extern bool pq_check_connection(void);