detect/sctp: add sctp.vtag keyword

Add a U32 numeric keyword to match the SCTP verification tag
from the common header with prefilter support.

Ticket #4251

src/Makefile.am

@@ -231,6 +231,7 @@ noinst_HEADERS = \
 	detect-sctphdr.h \
 	detect-sctp-chunk-cnt.h \
 	detect-sctp-chunk-type.h \
+	detect-sctp-vtag.h \
 	detect-ipaddr.h \
 	detect-ipopts.h \
 	detect-ipproto.h \
@@ -810,6 +811,7 @@ libsuricata_c_a_SOURCES = \
 	detect-sctphdr.c \
 	detect-sctp-chunk-cnt.c \
 	detect-sctp-chunk-type.c \
+	detect-sctp-vtag.c \
 	detect-ipaddr.c \
 	detect-ipopts.c \
 	detect-ipproto.c \

src/detect-engine-register.c

@@ -158,6 +158,7 @@
 #include "detect-sctphdr.h"
 #include "detect-sctp-chunk-type.h"
 #include "detect-sctp-chunk-cnt.h"
+#include "detect-sctp-vtag.h"
 #include "detect-urilen.h"
 #include "detect-bsize.h"
 #include "detect-detection-filter.h"
@@ -682,6 +683,7 @@ void SigTableSetup(void)
     DetectSCTPHdrRegister();
     DetectSCTPChunkTypeRegister();
     DetectSCTPChunkCntRegister();
+    DetectSCTPVtagRegister();
     DetectTlsRegister();
     DetectTlsValidityRegister();
     DetectTlsVersionRegister();

src/detect-engine-register.h

@@ -54,6 +54,7 @@ enum DetectKeywordId {
     DETECT_SCTPHDR,
     DETECT_SCTP_CHUNK_TYPE,
     DETECT_SCTP_CHUNK_CNT,
+    DETECT_SCTP_VTAG,
     DETECT_DSIZE,
 
     DETECT_FLOW,

src/detect-sctp-vtag.c

@@ -0,0 +1,129 @@
+/* Copyright (C) 2026 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
+ *
+ * Implements sctp.vtag keyword
+ *
+ * Author: Giuseppe Longo <glongo@oisf.net>
+ */
+
+#include "suricata-common.h"
+#include "decode.h"
+
+#include "detect.h"
+#include "detect-parse.h"
+#include "detect-engine.h"
+#include "detect-engine-prefilter.h"
+#include "detect-engine-prefilter-common.h"
+#include "detect-engine-build.h"
+#include "detect-engine-uint.h"
+
+#include "detect-sctp-vtag.h"
+
+#include "util-debug.h"
+
+static int DetectSCTPVtagSetup(DetectEngineCtx *, Signature *, const char *);
+static int DetectSCTPVtagMatch(
+        DetectEngineThreadCtx *, Packet *, const Signature *, const SigMatchCtx *);
+static void DetectSCTPVtagFree(DetectEngineCtx *, void *);
+static int PrefilterSetupSCTPVtag(DetectEngineCtx *de_ctx, SigGroupHead *sgh);
+static bool PrefilterSCTPVtagIsPrefilterable(const Signature *s);
+
+#ifdef UNITTESTS
+void DetectSCTPVtagRegisterTests(void);
+#endif
+
+void DetectSCTPVtagRegister(void)
+{
+    sigmatch_table[DETECT_SCTP_VTAG].name = "sctp.vtag";
+    sigmatch_table[DETECT_SCTP_VTAG].desc = "match on the SCTP verification tag";
+    sigmatch_table[DETECT_SCTP_VTAG].url = "/rules/sctp-keywords.html#sctp-vtag";
+    sigmatch_table[DETECT_SCTP_VTAG].Match = DetectSCTPVtagMatch;
+    sigmatch_table[DETECT_SCTP_VTAG].Setup = DetectSCTPVtagSetup;
+    sigmatch_table[DETECT_SCTP_VTAG].Free = DetectSCTPVtagFree;
+    sigmatch_table[DETECT_SCTP_VTAG].flags = SIGMATCH_INFO_UINT32;
+    sigmatch_table[DETECT_SCTP_VTAG].SupportsPrefilter = PrefilterSCTPVtagIsPrefilterable;
+    sigmatch_table[DETECT_SCTP_VTAG].SetupPrefilter = PrefilterSetupSCTPVtag;
+}
+
+static int DetectSCTPVtagMatch(
+        DetectEngineThreadCtx *det_ctx, Packet *p, const Signature *s, const SigMatchCtx *ctx)
+{
+    const DetectU32Data *data = (const DetectU32Data *)ctx;
+
+    DEBUG_VALIDATE_BUG_ON(PKT_IS_PSEUDOPKT(p));
+
+    if (!(PacketIsSCTP(p))) {
+        return 0;
+    }
+
+    return DetectU32Match(SCTP_GET_RAW_VTAG(PacketGetSCTP(p)), data);
+}
+
+static int DetectSCTPVtagSetup(DetectEngineCtx *de_ctx, Signature *s, const char *optstr)
+{
+    DetectU32Data *data = SCDetectU32Parse(optstr);
+    if (data == NULL)
+        return -1;
+
+    if (SCSigMatchAppendSMToList(
+                de_ctx, s, DETECT_SCTP_VTAG, (SigMatchCtx *)data, DETECT_SM_LIST_MATCH) == NULL) {
+        DetectSCTPVtagFree(de_ctx, data);
+        return -1;
+    }
+    s->flags |= SIG_FLAG_REQUIRE_PACKET;
+    return 0;
+}
+
+static void DetectSCTPVtagFree(DetectEngineCtx *de_ctx, void *ptr)
+{
+    SCDetectU32Free(ptr);
+}
+
+static void PrefilterPacketSCTPVtagMatch(
+        DetectEngineThreadCtx *det_ctx, Packet *p, const void *pectx)
+{
+    const PrefilterPacketHeaderCtx *ctx = pectx;
+
+    DEBUG_VALIDATE_BUG_ON(PKT_IS_PSEUDOPKT(p));
+    if (!PrefilterPacketHeaderExtraMatch(ctx, p))
+        return;
+
+    if (p->proto == IPPROTO_SCTP && PacketIsSCTP(p)) {
+        DetectU32Data du32;
+        du32.mode = ctx->v1.u8[0];
+        du32.arg1 = ctx->v1.u32[1];
+        du32.arg2 = ctx->v1.u32[2];
+        if (DetectU32Match(SCTP_GET_RAW_VTAG(PacketGetSCTP(p)), &du32)) {
+            SCLogDebug("packet matches SCTP vtag %u", ctx->v1.u32[0]);
+            PrefilterAddSids(&det_ctx->pmq, ctx->sigs_array, ctx->sigs_cnt);
+        }
+    }
+}
+
+static int PrefilterSetupSCTPVtag(DetectEngineCtx *de_ctx, SigGroupHead *sgh)
+{
+    return PrefilterSetupPacketHeader(de_ctx, sgh, DETECT_SCTP_VTAG, SIG_MASK_REQUIRE_REAL_PKT,
+            PrefilterPacketU32Set, PrefilterPacketU32Compare, PrefilterPacketSCTPVtagMatch);
+}
+
+static bool PrefilterSCTPVtagIsPrefilterable(const Signature *s)
+{
+    return PrefilterIsPrefilterableById(s, DETECT_SCTP_VTAG);
+}

src/detect-sctp-vtag.h

@@ -0,0 +1,27 @@
+/* Copyright (C) 2026 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
+ */
+
+#ifndef SURICATA_DETECT_SCTP_VTAG_H
+#define SURICATA_DETECT_SCTP_VTAG_H
+
+void DetectSCTPVtagRegister(void);
+
+#endif /* SURICATA_DETECT_SCTP_VTAG_H */