From 589d2ed4283130108df5495b5510d822282e1300 Mon Sep 17 00:00:00 2001 From: Oswald Buddenhagen Date: Wed, 14 Apr 2021 16:58:27 +0200 Subject: [PATCH] CVE-2021-3578: fix handling of unexpected APPENDUID response code if the code was sent in response to anything but a STORE, we'd overwrite a data pointer in one of our imap_cmd subclasses, an allocator data structure, or the start of the next allocation, with an int that was completely under the server's control. it's plausible that this could be exploited for remote code execution. to avoid this, we could ensure that the object is of the right type prior to casting, by using a new flag in the parameter block. but it's easier to just dispose of the out_uid field altogether and reuse the uid field that is present in the parameter block anyway, but was used only for FETCH commands so far. this problem was found by Lukas Braun using a fuzzer. --- src/drv_imap.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/src/drv_imap.c b/src/drv_imap.c index fbe2fed..4cc3b2a 100644 --- a/src/drv_imap.c +++ b/src/drv_imap.c @@ -181,7 +181,6 @@ typedef struct { imap_cmd_t gen; void (*callback)( int sts, uint uid, void *aux ); void *callback_aux; - uint out_uid; } imap_cmd_out_uid_t; typedef struct { @@ -1184,11 +1183,22 @@ parse_response_code( imap_store_t *ctx, imap_cmd_t *cmd, char *s ) */ for (; isspace( (uchar)*p ); p++); error( "*** IMAP ALERT *** %s\n", p ); - } else if (cmd && !strcmp( "APPENDUID", arg )) { + } else if (!strcmp( "APPENDUID", arg )) { + // The checks ensure that: + // - cmd => this is the final tagged response of a command, at which + // point cmd was already removed from ctx->in_progress, so param.uid + // is available for reuse. + // - !param.uid => the command isn't actually a FETCH. This doesn't + // really matter, as the field is safe to overwrite given the + // previous condition; it just has no effect for non-APPENDs. + if (!cmd || cmd->param.uid) { + error( "IMAP error: unexpected APPENDUID status\n" ); + return RESP_CANCEL; + } if (!(arg = next_arg( &s )) || (ctx->uidvalidity = strtoul( arg, &earg, 10 ), *earg) || !(arg = next_arg( &s )) || - (((imap_cmd_out_uid_t *)cmd)->out_uid = strtoul( arg, &earg, 10 ), *earg)) + (cmd->param.uid = strtoul( arg, &earg, 10 ), *earg)) { error( "IMAP error: malformed APPENDUID status\n" ); return RESP_CANCEL; @@ -2957,7 +2967,6 @@ imap_store_msg( store_t *gctx, msg_data_t *data, int to_trash, ctx->buffer_mem += data->len; cmd->gen.param.data_len = data->len; cmd->gen.param.data = data->data; - cmd->out_uid = 0; if (to_trash) { cmd->gen.param.create = 1; @@ -2990,7 +2999,7 @@ imap_store_msg_p2( imap_store_t *ctx ATTR_UNUSED, imap_cmd_t *cmd, int response imap_cmd_out_uid_t *cmdp = (imap_cmd_out_uid_t *)cmd; transform_msg_response( &response ); - cmdp->callback( response, cmdp->out_uid, cmdp->callback_aux ); + cmdp->callback( response, cmdp->gen.param.uid, cmdp->callback_aux ); } /******************* imap_find_new_msgs *******************/