diff --git a/src/internal.c b/src/internal.c
index fed9d370dea..39c7889132f 100644
--- a/src/internal.c
+++ b/src/internal.c
@@ -14280,9 +14280,19 @@ int CopyDecodedToX509(WOLFSSL_X509* x509, DecodedCert* dCert)
     /* if der contains original source buffer then store for potential
      * retrieval */
     if (dCert->source != NULL && dCert->maxIdx > 0) {
-        if (AllocDer(&x509->derCert, dCert->maxIdx, CERT_TYPE, x509->heap)
-                                                                         == 0) {
-            XMEMCPY(x509->derCert->buffer, dCert->source, dCert->maxIdx);
+        /* Store only the certificate itself, bounded by the end of its outer
+         * SEQUENCE (dCert->srcIdx), never any trailing bytes that may follow in
+         * the source buffer. This keeps wolfSSL_i2d_X509 / wolfSSL_X509_get_der
+         * / wolfSSL_X509_digest canonical - they operate on derCert - even on
+         * builds/paths that do not reject trailing data (e.g.
+         * WOLFSSL_NO_ASN_STRICT). It removes only bytes after the certificate,
+         * so the signed certificate bytes are preserved verbatim. */
+        word32 derCertSz = dCert->maxIdx;
+        if ((dCert->srcIdx > 0) && (dCert->srcIdx < derCertSz)) {
+            derCertSz = dCert->srcIdx;
+        }
+        if (AllocDer(&x509->derCert, derCertSz, CERT_TYPE, x509->heap) == 0) {
+            XMEMCPY(x509->derCert->buffer, dCert->source, derCertSz);
         }
         else {
             ret = MEMORY_E;
@@ -14618,9 +14628,14 @@ int CopyDecodedAcertToX509(WOLFSSL_X509_ACERT* x509, DecodedAcert* dAcert)
     /* if der contains original source buffer then store for potential
      * retrieval */
     if (dAcert->source != NULL && dAcert->maxIdx > 0) {
-        if (AllocDer(&x509->derCert, dAcert->maxIdx, CERT_TYPE, x509->heap)
-                                                                         == 0) {
-            XMEMCPY(x509->derCert->buffer, dAcert->source, dAcert->maxIdx);
+        /* Bound to the end of the attribute certificate's outer SEQUENCE so no
+         * trailing bytes after it are ever re-emitted by i2d / get_der. */
+        word32 derCertSz = dAcert->maxIdx;
+        if ((dAcert->srcIdx > 0) && (dAcert->srcIdx < derCertSz)) {
+            derCertSz = dAcert->srcIdx;
+        }
+        if (AllocDer(&x509->derCert, derCertSz, CERT_TYPE, x509->heap) == 0) {
+            XMEMCPY(x509->derCert->buffer, dAcert->source, derCertSz);
         }
         else {
             ret = MEMORY_E;
diff --git a/src/x509.c b/src/x509.c
index fd87b1da4aa..6059557d98b 100644
--- a/src/x509.c
+++ b/src/x509.c
@@ -6231,17 +6231,18 @@ static WOLFSSL_X509* loadX509orX509REQFromBuffer(
     /* ready to be decoded. */
     if (der != NULL && der->buffer != NULL) {
         WC_DECLARE_VAR(cert, DecodedCert, 1, 0);
-        /* For TRUSTED_CERT_TYPE, the DER buffer contains the certificate
-         * followed by auxiliary trust info. ParseCertRelative expects CERT_TYPE
-         * and will parse only the certificate portion, ignoring the rest. */
-        int parseType = (type == TRUSTED_CERT_TYPE) ? CERT_TYPE : type;
 
         WC_ALLOC_VAR_EX(cert, DecodedCert, 1, NULL, DYNAMIC_TYPE_DCERT,
             ret=MEMORY_ERROR);
         if (WC_VAR_OK(cert))
         {
             InitDecodedCert(cert, der->buffer, der->length, NULL);
-            ret = ParseCertRelative(cert, parseType, 0, NULL, NULL);
+            /* For TRUSTED_CERT_TYPE the DER buffer holds the certificate
+             * followed by auxiliary trust info. ParseCertRelative() recognizes
+             * the type: it parses only the certificate, permits the trailing
+             * aux data, and treats it as CERT_TYPE for verification. The DER is
+             * trimmed to the certificate below. */
+            ret = ParseCertRelative(cert, type, 0, NULL, NULL);
             if (ret == 0) {
                 /* For TRUSTED_CERT_TYPE, truncate the DER buffer to exclude
                  * auxiliary trust data. ParseCertRelative sets srcIdx to the
diff --git a/tests/api.c b/tests/api.c
index 32b90b9a079..4bca8a8c6a0 100644
--- a/tests/api.c
+++ b/tests/api.c
@@ -11792,6 +11792,10 @@ static int test_wc_CheckCertSigPubKey(void)
     ExpectNotNull(cert_der = (byte*)malloc(cert_dersz));
     ExpectIntGE(ret = wc_CertPemToDer(cert_buf, (int)cert_sz, cert_der,
         (int)cert_dersz, CERT_TYPE), 0);
+    /* Use the actual DER length, not the (larger) PEM buffer size, otherwise
+     * the decoded cert would have trailing bytes after its outer SEQUENCE. */
+    if (ret > 0)
+        cert_dersz = (word32)ret;
 
     wc_InitDecodedCert(&decoded, cert_der, cert_dersz, NULL);
     ExpectIntEQ(wc_ParseCert(&decoded, CERT_TYPE, NO_VERIFY, NULL), 0);
diff --git a/wolfcrypt/src/asn.c b/wolfcrypt/src/asn.c
index 7e855986f67..9feb3656b36 100644
--- a/wolfcrypt/src/asn.c
+++ b/wolfcrypt/src/asn.c
@@ -22020,6 +22020,35 @@ static int DecodeCertInternal(DecodedCert* cert, int verify, int* criticalExt,
         }
     }
 
+#ifndef WOLFSSL_NO_ASN_STRICT
+    /* Reject trailing data after the certificate's outer SEQUENCE.
+     *
+     * The template parser (GetASN_Items) only verifies that constructed items
+     * nested under the top-level item are fully consumed - it never checks that
+     * the outermost SEQUENCE spans all the way to maxIdx. Without this check,
+     * arbitrary bytes appended after a certificate are silently accepted and
+     * then returned/hashed verbatim by wolfSSL_i2d_X509 / wolfSSL_X509_get_der /
+     * wolfSSL_X509_digest (which operate on the stored source buffer of length
+     * maxIdx).
+     *
+     * cert->srcIdx points just past the certificate's outer SEQUENCE after the
+     * x509CertASN parse above. Only enforce this on a full parse; the
+     * pubkey-only paths (stopAtPubKey/stopAfterPubKey) intentionally parse the
+     * whole template but their callers may pass larger buffers. The TRUSTED
+     * CERTIFICATE format legitimately carries auxiliary trust data after the
+     * certificate, so allow it when cert->allowTrailing is set. */
+    if ((ret == 0) && (!done) && (!stopAtPubKey) && (!stopAfterPubKey) &&
+            (!cert->allowTrailing) && (cert->srcIdx != cert->maxIdx)
+#ifdef WOLFSSL_CERT_REQ
+            && (!cert->isCSR)
+#endif
+            ) {
+        WOLFSSL_MSG("Trailing data after certificate");
+        WOLFSSL_ERROR_VERBOSE(ASN_PARSE_E);
+        ret = ASN_PARSE_E;
+    }
+#endif /* !WOLFSSL_NO_ASN_STRICT */
+
     if ((ret == 0) && (!done) && (badDate != 0)) {
         /* Parsed whole certificate fine but return any date errors. */
         ret = badDate;
@@ -23169,6 +23198,17 @@ int ParseCertRelative(DecodedCert* cert, int type, int verify, void* cm,
         return BAD_FUNC_ARG;
     }
 
+    /* TRUSTED CERTIFICATE blobs (RFC/OpenSSL "TRUSTED CERTIFICATE") carry
+     * auxiliary trust data after the certificate. Permit that trailing data and
+     * parse only the certificate prefix; treat it as a normal certificate for
+     * all verification/path-length logic below. Doing this here (rather than in
+     * a single caller) means any caller of wc_ParseCert()/ParseCertRelative()
+     * that passes TRUSTED_CERT_TYPE gets the correct, consistent behavior. */
+    if (type == TRUSTED_CERT_TYPE) {
+        cert->allowTrailing = 1;
+        type = CERT_TYPE;
+    }
+
 #ifdef WOLFSSL_CERT_REQ
     if (type == CERTREQ_TYPE)
         cert->isCSR = 1;
diff --git a/wolfssl/wolfcrypt/asn.h b/wolfssl/wolfcrypt/asn.h
index 45993f0638a..5eec7d42d35 100644
--- a/wolfssl/wolfcrypt/asn.h
+++ b/wolfssl/wolfcrypt/asn.h
@@ -2067,6 +2067,10 @@ struct DecodedCert {
 
     /* Option Bits */
     WC_BITFIELD subjectCNStored:1;      /* have we saved a copy we own */
+    WC_BITFIELD allowTrailing:1;        /* permit data after the cert's outer
+                                         * SEQUENCE. Used internally for the
+                                         * TRUSTED CERTIFICATE auxiliary trust
+                                         * info. */
     WC_BITFIELD extSubjKeyIdSet:1;      /* Set when the SKID was read from cert */
     WC_BITFIELD extAuthKeyIdSet:1;      /* Set when the AKID was read from cert */
 #ifndef IGNORE_NAME_CONSTRAINTS