diff --git a/src/wp_aes_aead.c b/src/wp_aes_aead.c
index fb0893cb..75700cfc 100644
--- a/src/wp_aes_aead.c
+++ b/src/wp_aes_aead.c
@@ -458,6 +458,37 @@ static int wp_aead_get_ctx_params(wp_AeadCtx* ctx, OSSL_PARAM params[])
     return ok;
 }
 
+/**
+ * Check whether a tag length is one of the algorithm's allowed sizes.
+ *
+ * GCM tags must be 4, 8, 12, 13, 14, 15 or 16 bytes (NIST SP 800-38D).
+ * CCM tags must be 4, 6, 8, 10, 12, 14 or 16 bytes (NIST SP 800-38C /
+ * RFC 3610).
+ *
+ * @param [in] mode  Cipher mode: EVP_CIPH_GCM_MODE or EVP_CIPH_CCM_MODE.
+ * @param [in] sz    Tag length in bytes to check.
+ * @return  1 if sz is an allowed length for mode.
+ * @return  0 otherwise.
+ */
+static int wp_aead_tag_len_valid(int mode, size_t sz)
+{
+    int ok;
+
+    if (mode == EVP_CIPH_GCM_MODE) {
+        ok = (sz == 4) || (sz == 8) || (sz == 12) || (sz == 13) ||
+             (sz == 14) || (sz == 15) || (sz == 16);
+    }
+    else if (mode == EVP_CIPH_CCM_MODE) {
+        ok = (sz == 4) || (sz == 6) || (sz == 8) || (sz == 10) ||
+             (sz == 12) || (sz == 14) || (sz == 16);
+    }
+    else {
+        ok = 0;
+    }
+
+    return ok;
+}
+
 /**
  * Set the AEAD tag from the parameters.
  *
@@ -488,6 +519,9 @@ static int wp_aead_set_param_tag(wp_AeadCtx* ctx,
     if (ok && ((sz == 0) || ((p->data != NULL) && ctx->enc))) {
         ok = 0;
     }
+    if (ok && !wp_aead_tag_len_valid(ctx->mode, sz)) {
+        ok = 0;
+    }
     if (ok) {
         ctx->tagLen = sz;
     }
@@ -959,9 +993,10 @@ static int wp_aesgcm_tls_iv_set_fixed(wp_AeadCtx* ctx, unsigned char* iv,
     }
     else {
         /* Fixed field must be at least 4 bytes and invocation field at least 8
-         */
-        if ((len < EVP_GCM_TLS_FIXED_IV_LEN) ||
-            (ctx->ivLen - (int)len) < EVP_GCM_TLS_EXPLICIT_IV_LEN) {
+         * bytes */
+        if ((len < EVP_GCM_TLS_FIXED_IV_LEN) || (len > ctx->ivLen) ||
+            (len > sizeof(ctx->iv)) ||
+            (ctx->ivLen - len) < EVP_GCM_TLS_EXPLICIT_IV_LEN) {
                 return 0;
         }
         if (ctx->enc) {
diff --git a/test/test_aestag.c b/test/test_aestag.c
index ee9e2062..90edb00c 100644
--- a/test/test_aestag.c
+++ b/test/test_aestag.c
@@ -1416,6 +1416,159 @@ int test_aes_gcm_bad_tag(void *data)
     return err;
 }
 
+static int test_aes_gcm_tls_iv_fixed_oversized_helper(OSSL_LIB_CTX *libCtx,
+    const char *cipherName, int keyLen)
+{
+    int err;
+    EVP_CIPHER *cipher = NULL;
+    EVP_CIPHER_CTX *ctx = NULL;
+    unsigned char key[32];
+    /* ivLen (12, the GCM default) + EVP_GCM_TLS_EXPLICIT_IV_LEN (8) = 20: */
+    unsigned char iv[20];
+
+    memset(key, 0xCC, keyLen);
+    memset(iv, 0xDD, sizeof(iv));
+
+    cipher = EVP_CIPHER_fetch(libCtx, cipherName, "");
+    err = cipher == NULL;
+
+    /* A fixed len that leaves exactly the 8-byte
+     * explicit/invocation field must still be accepted. */
+    if (err == 0) {
+        ctx = EVP_CIPHER_CTX_new();
+        err = ctx == NULL;
+    }
+    if (err == 0) {
+        err = EVP_DecryptInit_ex(ctx, cipher, NULL, key, NULL) != 1;
+    }
+    if (err == 0) {
+        err = EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IV_FIXED,
+            EVP_GCM_TLS_FIXED_IV_LEN, iv) != 1;
+    }
+    EVP_CIPHER_CTX_free(ctx);
+    ctx = NULL;
+
+    /* Oversized fixed len (> ctx->ivLen, default 12) must be rejected. */
+    if (err == 0) {
+        ctx = EVP_CIPHER_CTX_new();
+        err = ctx == NULL;
+    }
+    if (err == 0) {
+        err = EVP_DecryptInit_ex(ctx, cipher, NULL, key, NULL) != 1;
+    }
+    if (err == 0) {
+        if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IV_FIXED,
+                (int)sizeof(iv), iv) == 1) {
+            PRINT_ERR_MSG("%s: EVP_CTRL_GCM_SET_IV_FIXED incorrectly "
+                          "accepted a fixed IV length (%d) larger than "
+                          "the IV length", cipherName, (int)sizeof(iv));
+            err = 1;
+        }
+    }
+
+    EVP_CIPHER_CTX_free(ctx);
+    EVP_CIPHER_free(cipher);
+    return err;
+}
+
+int test_aes_gcm_tls_iv_fixed_oversized(void *data)
+{
+    int err;
+
+    (void)data;
+
+    PRINT_MSG("AES-128-GCM TLS1 fixed-IV oversized length rejection");
+    err = test_aes_gcm_tls_iv_fixed_oversized_helper(wpLibCtx,
+        "AES-128-GCM", 16);
+
+    return err;
+}
+
+/*
+ * Test that GCM tags smaller than the 32-bit minimum are rejected.
+ */
+static int test_aes_gcm_tag_len_undersized_helper(OSSL_LIB_CTX *libCtx,
+    const char *cipherName, int keyLen)
+{
+    int err;
+    EVP_CIPHER *cipher = NULL;
+    EVP_CIPHER_CTX *ctx = NULL;
+    unsigned char key[32];
+    unsigned char iv[12];
+    unsigned char aad[] = "additional data";
+    unsigned char pt[] = "GCM plaintext for tag length test";
+    int ptLen = (int)(sizeof(pt) - 1);
+    unsigned char ct[64];
+    unsigned char tag[16];
+    int outLen = 0, fLen = 0;
+
+    memset(key, 0xAA, keyLen);
+    memset(iv, 0xBB, sizeof(iv));
+
+    cipher = EVP_CIPHER_fetch(libCtx, cipherName, "");
+    err = cipher == NULL;
+
+    /* Encrypt normally to get a valid ciphertext/full-size tag pair. */
+    if (err == 0) {
+        ctx = EVP_CIPHER_CTX_new();
+        err = ctx == NULL;
+    }
+    if (err == 0) {
+        err = EVP_EncryptInit(ctx, cipher, key, iv) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptUpdate(ctx, NULL, &outLen, aad,
+                                (int)(sizeof(aad) - 1)) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptUpdate(ctx, ct, &outLen, pt, ptLen) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptFinal_ex(ctx, ct + outLen, &fLen) != 1;
+        outLen += fLen;
+    }
+    if (err == 0) {
+        err = EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, sizeof(tag),
+                                  tag) != 1;
+    }
+    EVP_CIPHER_CTX_free(ctx);
+    ctx = NULL;
+
+    /* A 1-byte tag length is below the NIST-mandated minimum (4 bytes)
+     * and must be rejected here. */
+    if (err == 0) {
+        ctx = EVP_CIPHER_CTX_new();
+        err = ctx == NULL;
+    }
+    if (err == 0) {
+        err = EVP_DecryptInit(ctx, cipher, NULL, NULL) != 1;
+    }
+    if (err == 0) {
+        if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, 1, tag) == 1) {
+            PRINT_ERR_MSG("%s: EVP_CTRL_AEAD_SET_TAG incorrectly accepted "
+                          "a 1-byte tag length", cipherName);
+            err = 1;
+        }
+    }
+
+    EVP_CIPHER_CTX_free(ctx);
+    EVP_CIPHER_free(cipher);
+    return err;
+}
+
+int test_aes_gcm_tag_len_undersized(void *data)
+{
+    int err;
+
+    (void)data;
+
+    PRINT_MSG("AES-128-GCM undersized tag length rejection");
+    err = test_aes_gcm_tag_len_undersized_helper(wpLibCtx, "AES-128-GCM",
+        16);
+
+    return err;
+}
+
 #endif /* WP_HAVE_AESGCM */
 
 /******************************************************************************/
@@ -1601,5 +1754,108 @@ int test_aes_ccm_bad_tag(void *data)
     return err;
 }
 
+/*
+ * Test that CCM tags are at least 32 bits.
+ */
+static int test_aes_ccm_tag_len_undersized_helper(OSSL_LIB_CTX *libCtx,
+    const char *cipherName, int keyLen)
+{
+    int err;
+    EVP_CIPHER *cipher = NULL;
+    EVP_CIPHER_CTX *ctx = NULL;
+    unsigned char key[32];
+    unsigned char iv[13];
+    unsigned char aad[] = "additional data";
+    unsigned char pt[] = "CCM plaintext for tag length test";
+    int ptLen = (int)(sizeof(pt) - 1);
+    unsigned char ct[64];
+    unsigned char tag[16];
+    int outLen = 0, fLen = 0;
+
+    memset(key, 0xAA, keyLen);
+    memset(iv, 0xBB, sizeof(iv));
+
+    cipher = EVP_CIPHER_fetch(libCtx, cipherName, "");
+    err = cipher == NULL;
+
+    /* Encrypt normally to get a valid ciphertext/full-size tag pair. */
+    if (err == 0) {
+        ctx = EVP_CIPHER_CTX_new();
+        err = ctx == NULL;
+    }
+    if (err == 0) {
+        err = EVP_EncryptInit(ctx, cipher, NULL, NULL) != 1;
+    }
+    if (err == 0) {
+        err = EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN,
+                                  (int)sizeof(iv), NULL) != 1;
+    }
+    if (err == 0) {
+        err = EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, sizeof(tag),
+                                  NULL) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptInit(ctx, NULL, key, iv) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptUpdate(ctx, NULL, &outLen, NULL, ptLen) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptUpdate(ctx, NULL, &outLen, aad,
+                                (int)(sizeof(aad) - 1)) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptUpdate(ctx, ct, &outLen, pt, ptLen) != 1;
+    }
+    if (err == 0) {
+        err = EVP_EncryptFinal_ex(ctx, ct + outLen, &fLen) != 1;
+        outLen += fLen;
+    }
+    if (err == 0) {
+        err = EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, sizeof(tag),
+                                  tag) != 1;
+    }
+    EVP_CIPHER_CTX_free(ctx);
+    ctx = NULL;
+
+    /* A 1-byte tag length is below the NIST-mandated minimum (4 bytes)
+     * and must be rejected here. */
+    if (err == 0) {
+        ctx = EVP_CIPHER_CTX_new();
+        err = ctx == NULL;
+    }
+    if (err == 0) {
+        err = EVP_DecryptInit(ctx, cipher, NULL, NULL) != 1;
+    }
+    if (err == 0) {
+        err = EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN,
+                                  (int)sizeof(iv), NULL) != 1;
+    }
+    if (err == 0) {
+        if (EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, 1, tag) == 1) {
+            PRINT_ERR_MSG("%s: EVP_CTRL_AEAD_SET_TAG incorrectly accepted "
+                          "a 1-byte tag length", cipherName);
+            err = 1;
+        }
+    }
+
+    EVP_CIPHER_CTX_free(ctx);
+    EVP_CIPHER_free(cipher);
+    return err;
+}
+
+int test_aes_ccm_tag_len_undersized(void *data)
+{
+    int err;
+
+    (void)data;
+
+    PRINT_MSG("AES-128-CCM undersized tag length rejection");
+    err = test_aes_ccm_tag_len_undersized_helper(wpLibCtx, "AES-128-CCM",
+        16);
+
+    return err;
+}
+
 #endif /* WP_HAVE_AESCCM */
 
diff --git a/test/unit.c b/test/unit.c
index e116f9b5..cb02a4b9 100644
--- a/test/unit.c
+++ b/test/unit.c
@@ -288,6 +288,8 @@ TEST_CASE test_case[] = {
     TEST_DECL(test_aes128_gcm_set_iv_inv, NULL),
     TEST_DECL(test_aes128_gcm_key_then_iv, NULL),
     TEST_DECL(test_aes_gcm_bad_tag, NULL),
+    TEST_DECL(test_aes_gcm_tls_iv_fixed_oversized, NULL),
+    TEST_DECL(test_aes_gcm_tag_len_undersized, NULL),
 #endif
 #ifdef WP_HAVE_AESCCM
     TEST_DECL(test_aes128_ccm, NULL),
@@ -296,6 +298,7 @@ TEST_CASE test_case[] = {
 #if OPENSSL_VERSION_NUMBER >= 0x10100000L
     TEST_DECL(test_aes128_ccm_tls, NULL),
     TEST_DECL(test_aes_ccm_bad_tag, NULL),
+    TEST_DECL(test_aes_ccm_tag_len_undersized, NULL),
 #endif
 #endif
 #ifdef WP_HAVE_RANDOM
diff --git a/test/unit.h b/test/unit.h
index 9aab6828..26b6349d 100644
--- a/test/unit.h
+++ b/test/unit.h
@@ -219,6 +219,8 @@ int test_aes128_gcm_tls(void *data);
 int test_aes128_gcm_set_iv_inv(void *data);
 int test_aes128_gcm_key_then_iv(void *data);
 int test_aes_gcm_bad_tag(void *data);
+int test_aes_gcm_tls_iv_fixed_oversized(void *data);
+int test_aes_gcm_tag_len_undersized(void *data);
 
 #endif /* WP_HAVE_AESGCM */
 
@@ -229,6 +231,7 @@ int test_aes192_ccm(void *data);
 int test_aes256_ccm(void *data);
 int test_aes128_ccm_tls(void *data);
 int test_aes_ccm_bad_tag(void *data);
+int test_aes_ccm_tag_len_undersized(void *data);
 
 #endif /* WP_HAVE_AESCCM */