suricata/src/app-layer-imap.c

/* Copyright (C) 2024 Open Information Security Foundation
 *
 * You can copy, redistribute or modify this Program under the terms of
 * the GNU General Public License version 2 as published by the Free
 * Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * version 2 along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

/**
 * \file
 *
 * \author Mahmoud Maatuq <mahmoudmatook.mm@gmail.com>
 *
 */

#include "suricata-common.h"
#include "app-layer-detect-proto.h"
#include "app-layer-imap.h"
#include "app-layer-protos.h"
#include "rust.h"
#include "stream-tcp-private.h"
#include "stream-tcp-reassemble.h"
#include "util-debug.h"

static AppProto ImapClientProbingParser(
        const Flow *f, uint8_t direction, const uint8_t *input, uint32_t len, uint8_t *rdir)
{
    // This is called after " CAPABILITY" pattern has been found
    if (f->alproto_tc == ALPROTO_IMAP) {
        // server was already recognised as IMAP, so ok
        return ALPROTO_IMAP;
    }
    for (size_t i = 0; i < len; i++) {
        if (input[i] >= '0' && input[i] <= '9') {
            // We check if the tag at the beginning of the input contains a number
            return ALPROTO_IMAP;
        }
        if (input[i] == ' ') {
            break;
        }
    }

    TcpSession *ssn = (TcpSession *)f->protoctx;
    if (ssn == NULL) {
        return ALPROTO_FAILED;
    }
    const uint32_t size_tc = StreamDataAvailableForProtoDetect(&ssn->server);

    if (size_tc < 8 && f->alproto_tc == ALPROTO_UNKNOWN) {
        // wait for another packet from server
        return ALPROTO_UNKNOWN;
    }
    return ALPROTO_FAILED;
}

static int IMAPRegisterPatternsForProtocolDetection(void)
{
    if (SCAppLayerProtoDetectPMRegisterPatternCI(
                IPPROTO_TCP, ALPROTO_IMAP, "* OK ", 5, 0, STREAM_TOCLIENT) < 0) {
        return -1;
    }

    if (SCAppLayerProtoDetectPMRegisterPatternCI(
                IPPROTO_TCP, ALPROTO_IMAP, "* NO ", 5, 0, STREAM_TOCLIENT) < 0) {
        return -1;
    }

    if (SCAppLayerProtoDetectPMRegisterPatternCI(
                IPPROTO_TCP, ALPROTO_IMAP, "* BAD ", 6, 0, STREAM_TOCLIENT) < 0) {
        return -1;
    }

    if (SCAppLayerProtoDetectPMRegisterPatternCI(
                IPPROTO_TCP, ALPROTO_IMAP, "* LIST ", 7, 0, STREAM_TOCLIENT) < 0) {
        return -1;
    }

    if (SCAppLayerProtoDetectPMRegisterPatternCI(
                IPPROTO_TCP, ALPROTO_IMAP, "* ESEARCH ", 10, 0, STREAM_TOCLIENT) < 0) {
        return -1;
    }

    if (SCAppLayerProtoDetectPMRegisterPatternCI(
                IPPROTO_TCP, ALPROTO_IMAP, "* STATUS ", 9, 0, STREAM_TOCLIENT) < 0) {
        return -1;
    }

    if (SCAppLayerProtoDetectPMRegisterPatternCI(
                IPPROTO_TCP, ALPROTO_IMAP, "* FLAGS ", 8, 0, STREAM_TOCLIENT) < 0) {
        return -1;
    }

    /**
     * there is no official document that limits the length of the tag
     * some practical implementations limit it to 20 characters
     * but keeping depth equal to 31 fails unit tests such  AppLayerTest10
     * so keeping depth 17 for now to pass unit tests, that might miss some detections
     * until we find a better solution for the unit tests.
     *
     * AppLayerTest10 fails because it expects protocol detection to be completed with only 17 bytes
     * as input, and with this new pattern, we would need more bytes to finish protocol detection.
     */
    if (SCAppLayerProtoDetectPMRegisterPatternCIwPP(IPPROTO_TCP, ALPROTO_IMAP, " CAPABILITY",
                17 /*6 for max tag len + space + len(CAPABILITY)*/, 0, STREAM_TOSERVER,
                ImapClientProbingParser, 12, 17) < 0) {
        return -1;
    }

    return 0;
}

void RegisterIMAPParsers(void)
{
    const char *proto_name = "imap";

    if (SCAppLayerProtoDetectConfProtoDetectionEnabled("tcp", proto_name)) {
        SCLogDebug("IMAP protocol detection is enabled.");
        AppLayerProtoDetectRegisterProtocol(ALPROTO_IMAP, proto_name);
        if (IMAPRegisterPatternsForProtocolDetection() < 0)
            SCLogError("Failed to register IMAP protocol detection patterns.");
    } else {
        SCLogDebug("Protocol detector and parser disabled for IMAP.");
    }
}