diff --git a/apps/wolfssh/common.c b/apps/wolfssh/common.c
index ac1adc4e0..af635bb4a 100644
--- a/apps/wolfssh/common.c
+++ b/apps/wolfssh/common.c
@@ -391,12 +391,18 @@ int ClientPublicKeyCheck(const byte* pubKey, word32 pubKeySz, void* ctx)
         pubKeyType[0] = 0;
         fp[0] = 0;
 
-        /* Get the key type out of the key. */
-        ato32(pubKey, &sz);
-        if ((sz > pubKeySz - sizeof(word32))
-                    || (sz > WOLFSSH_CLIENT_PUBKEYTYPE_SIZE_ESTIMATE - 1)) {
+        /* Get the key type out of the key. Require at least a word32
+         * length prefix to avoid an unsigned underflow below. */
+        if (pubKeySz < (word32)sizeof(word32)) {
             ret = -1;
         }
+        else {
+            ato32(pubKey, &sz);
+            if ((sz > pubKeySz - sizeof(word32))
+                        || (sz > WOLFSSH_CLIENT_PUBKEYTYPE_SIZE_ESTIMATE - 1)) {
+                ret = -1;
+            }
+        }
     }
 
     if (ret == 0) {
diff --git a/src/agent.c b/src/agent.c
index 7b7ac5c5d..2e562001e 100644
--- a/src/agent.c
+++ b/src/agent.c
@@ -672,7 +672,8 @@ static WOLFSSH_AGENT_ID* FindKeyId(WOLFSSH_AGENT_ID* id,
     if (ret == WS_SUCCESS) {
         while (id != NULL &&
                 WMEMCMP(digest, id->id, WC_SHA256_DIGEST_SIZE) != 0 &&
-                WMEMCMP(keyBlob, id->keyBlob, keyBlobSz)) {
+                (keyBlobSz != id->keyBlobSz ||
+                 WMEMCMP(keyBlob, id->keyBlob, keyBlobSz) != 0)) {
             id = id->next;
         }
     }
@@ -1386,7 +1387,7 @@ static int DoMessage(WOLFSSH_AGENT_CTX* agent,
         ato32(buf + begin, &payloadSz);
         WLOG(WS_LOG_AGENT, "payloadSz = %u", payloadSz);
         begin += LENGTH_SZ;
-        if (payloadSz > len - begin) {
+        if (payloadSz == 0 || payloadSz > len - begin) {
             ret = WS_OVERFLOW_E;
         }
     }
diff --git a/src/internal.c b/src/internal.c
index 8b7fd28cc..6e8ab9fb5 100644
--- a/src/internal.c
+++ b/src/internal.c
@@ -3509,6 +3509,12 @@ WOLFSSH_CHANNEL* ChannelNew(WOLFSSH* ssh, byte channelType,
                 WMEMSET(newChannel, 0, sizeof(WOLFSSH_CHANNEL));
                 newChannel->ssh = ssh;
                 newChannel->channelType = channelType;
+                /* Skip channel ids already in use to avoid collisions when
+                 * nextChannel (word32) wraps around. */
+                while (ChannelFind(ssh, ssh->nextChannel,
+                                   WS_CHANNEL_ID_SELF) != NULL) {
+                    ssh->nextChannel++;
+                }
                 newChannel->channel = ssh->nextChannel++;
                 WLOG(WS_LOG_DEBUG, "New channel id = %u", newChannel->channel);
                 newChannel->windowSz = initialWindowSz;
@@ -4415,7 +4421,7 @@ static int GetNameList(byte* idList, word32* idListSz,
      */
 
     if (ret == WS_SUCCESS) {
-        if (*idx >= len || *idx + 4 >= len)
+        if (*idx >= len || *idx + 4 > len)
             ret = WS_BUFFER_E;
     }
 
@@ -7023,7 +7029,8 @@ static int DoKexDhReply(WOLFSSH* ssh, byte* buf, word32 len, word32* idx)
             if (ret == WS_SUCCESS) {
                 /* Check that scratch isn't larger than the remainder of the
                  * sig buffer and leaves enough room for another length. */
-                if (scratch > sigSz - begin - LENGTH_SZ) {
+                if (begin + LENGTH_SZ > sigSz ||
+                        scratch > sigSz - begin - LENGTH_SZ) {
                     WLOG(WS_LOG_DEBUG, "sig name size is too large");
                     ret = WS_PARSE_E;
                 }
@@ -12362,6 +12369,10 @@ static int BuildNameList(char* buf, word32 bufSz,
 
     idx = 0;
 
+    if (srcSz == 0) {
+        return 0;
+    }
+
     do {
         name = IdToName(*src);
         nameSz = (int)WSTRLEN(name);
@@ -18773,7 +18784,12 @@ int SendChannelData(WOLFSSH* ssh, word32 channelId,
         word32 bound = min(channel->peerWindowSz, channel->peerMaxPacketSz);
         bound = min(bound, channel->maxPacketSz);
 
-        if (dataSz > bound) {
+        if (bound == 0 && dataSz != 0) {
+            WLOG(WS_LOG_DEBUG, "peer max packet size is zero");
+            ssh->error = WS_WINDOW_FULL;
+            ret = WS_WINDOW_FULL;
+        }
+        else if (dataSz > bound) {
             WLOG(WS_LOG_DEBUG,
                  "Trying to send %u, client will only accept %u, limiting",
                  dataSz, bound);
@@ -18886,7 +18902,12 @@ int SendChannelExtendedData(WOLFSSH* ssh, word32 channelId,
         word32 bound = min(channel->peerWindowSz, channel->peerMaxPacketSz);
         bound = min(bound, channel->maxPacketSz);
 
-        if (dataSz > bound) {
+        if (bound == 0 && dataSz != 0) {
+            WLOG(WS_LOG_DEBUG, "peer max packet size is zero");
+            ssh->error = WS_WINDOW_FULL;
+            ret = WS_WINDOW_FULL;
+        }
+        else if (dataSz > bound) {
             WLOG(WS_LOG_DEBUG,
                  "Trying to send %u, client will only accept %u, limiting",
                  dataSz, bound);
diff --git a/src/ssh.c b/src/ssh.c
index f73754e92..c3dcba3c6 100644
--- a/src/ssh.c
+++ b/src/ssh.c
@@ -3835,7 +3835,8 @@ int wolfSSH_RealPath(const char* defaultPath, char* in,
         }
         /* Everything else is copied */
         else {
-            if (curSz >= outSz - segSz) {
+            if (segSz == 0 || segSz >= outSz ||
+                    curSz >= outSz - segSz - (curSz != 1 ? 1 : 0)) {
                 return WS_INVALID_PATH_E;
             }
 
diff --git a/src/wolfsftp.c b/src/wolfsftp.c
index 9d4671834..2d9f81182 100644
--- a/src/wolfsftp.c
+++ b/src/wolfsftp.c
@@ -6634,6 +6634,14 @@ static int wolfSSH_SFTP_DoStatus(WOLFSSH* ssh, word32 reqId,
         return WS_FATAL_ERROR;
     }
 
+    /* status is a small enumerated value (0..WOLFSSH_FTP_UNSUPPORTED). An
+     * out-of-range value from a malicious or broken server must not be
+     * returned as a negative int, where it would alias an internal WS_*
+     * error code and bypass the WOLFSSH_FTP_* classification in callers. */
+    if (status > (word32)WOLFSSH_FTP_UNSUPPORTED) {
+        status = WOLFSSH_FTP_FAILURE;
+    }
+
     /* read error message */
     if (GetStringRef(&sz, &str, buf, maxIdx, &localIdx) != WS_SUCCESS) {
         return WS_FATAL_ERROR;