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authorTom Lane2021-11-08 16:01:43 +0000
committerTom Lane2021-11-08 16:01:43 +0000
commite92ed93e8eb76ee0701b42d4f0ce94e6af3fc741 (patch)
tree747c7536594cfb590e0b56a6cdf92c6d2c7defe9
parent7c0a78f089980cec45927aa3160add1781aed402 (diff)
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
-rw-r--r--src/backend/libpq/pqcomm.c12
-rw-r--r--src/backend/postmaster/postmaster.c24
-rw-r--r--src/include/libpq/libpq.h1
3 files changed, 37 insertions, 0 deletions
diff --git a/src/backend/libpq/pqcomm.c b/src/backend/libpq/pqcomm.c
index ee2cd86866d..93f2e0b81d3 100644
--- a/src/backend/libpq/pqcomm.c
+++ b/src/backend/libpq/pqcomm.c
@@ -1183,6 +1183,18 @@ pq_getstring(StringInfo s)
}
}
+/* --------------------------------
+ * 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 5775fc0c091..1e0936e5b48 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -2050,6 +2050,18 @@ retry1:
#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
* follow if SSL was rejected (client may negotiate in either order)
@@ -2082,6 +2094,18 @@ retry1:
#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
* follow if GSS was rejected (client may negotiate in either order)
diff --git a/src/include/libpq/libpq.h b/src/include/libpq/libpq.h
index b1152475ace..54c5fa77977 100644
--- a/src/include/libpq/libpq.h
+++ b/src/include/libpq/libpq.h
@@ -72,6 +72,7 @@ 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_putbytes(const char *s, size_t len);
/*