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fix: harden bounds/underflow paths in wolfSSH #1096

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Merged
JacobBarthelmeh merged 4 commits into from
Jul 28, 2026
Merged

fix: harden bounds/underflow paths in wolfSSH #1096

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7316e71
fix: harden bounds/underflow paths in wolfSSH
MarkAtwood Jul 10, 2026
3966e89
Parse the agent message header with GetSize
ejohnstown Jul 25, 2026
3141c7d
tests: cover the zero bound, empty name list, and short sig blob
ejohnstown Jul 25, 2026
00880c6
Clean up two source comments
ejohnstown Jul 25, 2026
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24 changes: 9 additions & 15 deletions src/agent.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1392,24 +1392,18 @@ static int DoMessage(WOLFSSH_AGENT_CTX* agent,
if (ret == WS_SUCCESS) {
WLOG(WS_LOG_AGENT, "len = %u, idx = %u", len, *idx);
begin = *idx;
if (begin > len) {
ret = WS_OVERFLOW_E;
}
}

if (ret == WS_SUCCESS) {
if (LENGTH_SZ + MSG_ID_SZ + begin > len) {
/* GetSize bounds the prefix and the payload; a nonzero payloadSz
* then covers the msg id read below. Reject 0: payloadSz - 1 is
* used as a length. */
if (GetSize(&payloadSz, buf, len, &begin) != WS_SUCCESS) {
ret = WS_OVERFLOW_E;
}
}

if (ret == WS_SUCCESS) {
ato32(buf + begin, &payloadSz);
WLOG(WS_LOG_AGENT, "payloadSz = %u", payloadSz);
begin += LENGTH_SZ;
/* reject 0: payloadSz - 1 is used as a length below */
if (payloadSz == 0 || payloadSz > len - begin) {
ret = WS_OVERFLOW_E;
else {
WLOG(WS_LOG_AGENT, "payloadSz = %u", payloadSz);
if (payloadSz == 0) {
ret = WS_OVERFLOW_E;
}
}
}

Expand Down
114 changes: 63 additions & 51 deletions src/internal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3606,6 +3606,12 @@ 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;
Expand Down Expand Up @@ -4552,11 +4558,7 @@ static int GetNameList(byte* idList, word32* idListSz,
*/

if (ret == WS_SUCCESS) {
if (*idx >= len || *idx + 4 >= len)
ret = WS_BUFFER_E;
}

if (ret == WS_SUCCESS) {
/* GetStringRef bounds the length prefix and the list. */
ret = GetStringRef(&nameListSz, &nameList, buf, len, idx);
}

Expand Down Expand Up @@ -6934,7 +6936,6 @@ static int DoKexDhReply(WOLFSSH* ssh, byte* buf, word32 len, word32* idx)
word32 pubKeySz;
word32 fSz;
word32 sigSz;
word32 scratch;
word32 begin;
int ret = WS_SUCCESS;
enum wc_HashType hashId;
Expand Down Expand Up @@ -7176,47 +7177,36 @@ static int DoKexDhReply(WOLFSSH* ssh, byte* buf, word32 len, word32* idx)

/* Verify h with the server's public key. */
if (ret == WS_SUCCESS) {
#ifndef WOLFSSH_NO_RSA
int tmpIdx = begin - sigSz;
#endif
const char* expectedSigName =
IdToName(SigTypeForId(ssh->handshake->pubKeyId));
word32 expectedSigNameSz = (word32)WSTRLEN(expectedSigName);
const byte* sigName = NULL;
word32 sigNameSz = 0;
word32 sigBlobSz = 0;

begin = 0;
ret = GetUint32(&scratch, sig, sigSz, &begin);
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) {
WLOG(WS_LOG_DEBUG, "sig name size is too large");
ret = WS_PARSE_E;
}
}
ret = GetStringRef(&sigNameSz, &sigName, sig, sigSz, &begin);
if (ret == WS_SUCCESS) {
if (scratch != expectedSigNameSz ||
WMEMCMP(sig + begin, expectedSigName, scratch) != 0) {
/* expectedSigName is never empty, so a null sigName fails
* on size first. */
if (sigNameSz != expectedSigNameSz ||
WMEMCMP(sigName, expectedSigName, sigNameSz) != 0) {
WLOG(WS_LOG_DEBUG,
"signature name %.*s did not match negotiated %s",
(int)scratch, (const char*)(sig + begin),
(int)sigNameSz,
(sigName != NULL) ? (const char*)sigName : "",
expectedSigName);
ret = WS_PARSE_E;
}
}
if (ret == WS_SUCCESS) {
begin += scratch;
ret = GetUint32(&scratch, sig, sigSz, &begin);
}
if (ret == WS_SUCCESS) {
if (scratch > sigSz - begin) {
WLOG(WS_LOG_DEBUG, "sig name size is too large");
ret = WS_PARSE_E;
}
/* GetSize leaves begin at the blob, and sig non-null when
* the blob is empty. */
ret = GetSize(&sigBlobSz, sig, sigSz, &begin);
}
if (ret == WS_SUCCESS) {
sig = sig + begin;
/* In the fuzz, sigSz ends up 1 and it has issues. */
sigSz = scratch;
sigSz = sigBlobSz;

if (sigKeyBlock_ptr->useRsa) {
#ifndef WOLFSSH_NO_RSA
Expand All @@ -7225,12 +7215,6 @@ static int DoKexDhReply(WOLFSSH* ssh, byte* buf, word32 len, word32* idx)
ret = WS_RSA_E;
}

if (sigSz + begin + tmpIdx > len) {
WLOG(WS_LOG_DEBUG,
"Signature size found would result in error 2");
ret = WS_BUFFER_E;
}

if (ret == WS_SUCCESS) {
ret = wc_SignatureVerify(
HashForId(ssh->handshake->pubKeyId),
Expand Down Expand Up @@ -12771,6 +12755,14 @@ static int BuildNameList(char* buf, word32 bufSz,

idx = 0;

if (srcSz == 0) {
/* Terminate: callers measure buf with WSTRLEN. */
if (buf != NULL && bufSz > 0) {
buf[0] = '\0';
}
return 0;
}

do {
name = IdToName(*src);
nameSz = (int)WSTRLEN(name);
Expand Down Expand Up @@ -19431,15 +19423,22 @@ int SendChannelData(WOLFSSH* ssh, word32 channelId,
word32 bound = min(channel->peerWindowSz, channel->peerMaxPacketSz);
bound = min(bound, channel->maxPacketSz);

if (dataSz > bound) {
WLOG(WS_LOG_DEBUG,
"Trying to send %u, client will only accept %u, limiting",
dataSz, bound);
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);
dataSz = bound;
}

ret = PreparePacket(ssh,
MSG_ID_SZ + UINT32_SZ + LENGTH_SZ + dataSz);
ret = PreparePacket(ssh,
MSG_ID_SZ + UINT32_SZ + LENGTH_SZ + dataSz);
}
}

if (ret == WS_SUCCESS) {
Expand Down Expand Up @@ -19544,15 +19543,22 @@ int SendChannelExtendedData(WOLFSSH* ssh, word32 channelId,
word32 bound = min(channel->peerWindowSz, channel->peerMaxPacketSz);
bound = min(bound, channel->maxPacketSz);

if (dataSz > bound) {
WLOG(WS_LOG_DEBUG,
"Trying to send %u, client will only accept %u, limiting",
dataSz, bound);
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);
dataSz = bound;
}

ret = PreparePacket(ssh,
MSG_ID_SZ + UINT32_SZ + UINT32_SZ + LENGTH_SZ + dataSz);
ret = PreparePacket(ssh,
MSG_ID_SZ + UINT32_SZ + UINT32_SZ + LENGTH_SZ + dataSz);
}
}

if (ret == WS_SUCCESS) {
Expand Down Expand Up @@ -20625,6 +20631,12 @@ int wolfSSH_TestChannelPutData(WOLFSSH_CHANNEL* channel, byte* data,
return ChannelPutData(channel, data, dataSz);
}

int wolfSSH_TestBuildNameList(char* buf, word32 bufSz,
const byte* src, word32 srcSz)
{
return BuildNameList(buf, bufSz, src, srcSz);
}

int wolfSSH_TestDoChannelSuccess(WOLFSSH* ssh, byte* buf, word32 len,
word32* idx)
{
Expand Down
8 changes: 8 additions & 0 deletions src/wolfsftp.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6636,6 +6636,14 @@ 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;
Expand Down
31 changes: 31 additions & 0 deletions tests/regress.c
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Expand Up @@ -425,6 +425,7 @@ static word32 LoadFileBuffer(const char* path, byte* buf, word32 bufSz)
/* KEXDH_REPLY mutation modes for the duplex mutator. */
#define REGRESS_MUTATE_SIG_NAME 0
#define REGRESS_MUTATE_SIG_DATA 1
#define REGRESS_MUTATE_SIG_NAME_OVERRUN 2

typedef struct {
byte data[REGRESS_DUPLEX_QUEUE_SZ];
Expand Down Expand Up @@ -676,6 +677,12 @@ static int RewriteSingleKexDhReplyPacket(const byte* packet, word32 packetSz,
}
innerSig[flipIdx] ^= 0xFF;
}
else if (mode == REGRESS_MUTATE_SIG_NAME_OVERRUN) {
/* Nothing but a name length prefix, so the name it claims runs off
* the end of the blob. */
innerSigSz = AppendUint32(innerSig, sizeof(innerSig), innerSigSz,
sigNameSz);
}
else {
innerSigSz = AppendString(innerSig, sizeof(innerSig), innerSigSz,
replacement);
Expand Down Expand Up @@ -1149,6 +1156,29 @@ static void TestKexDhReplyRejectsEd25519CorruptSig(void)
}
#endif

/* A signature blob holding only a name length prefix. The bounded read
* rejects it before the name is compared, whatever the host key type. */
static void TestKexDhReplyRejectsSigNameOverrun(void)
{
KexReplyHarness harness;
KexReplyRunResult result;

InitKexReplyHarnessEx(&harness, REGRESS_DEFAULT_KEY_ALGO,
REGRESS_DEFAULT_KEY_PATH, 1,
REGRESS_MUTATE_SIG_NAME_OVERRUN, NULL, 0);
RunKexReplyHandshake(&harness, &result);

AssertIntEQ(harness.mutator.parseError, 0);
AssertIntEQ(harness.mutator.matchedPackets, 1);
AssertIntEQ(harness.mutator.mutatedPackets, 1);
AssertFalse(result.clientSuccess);
AssertFalse(harness.client->connectState >= CONNECT_KEYED);
AssertTrue(result.clientRet == WS_FATAL_ERROR);
AssertIntEQ(result.clientErr, WS_BUFFER_E);

FreeKexReplyHarness(&harness);
}

#endif /* KEXDH_REPLY_REGRESS_KEX_ALGO */

static word32 ParseChannelOpenFailRecipient(const byte* pkt, word32 sz)
Expand Down Expand Up @@ -5175,6 +5205,7 @@ int main(int argc, char** argv)
#ifndef WOLFSSH_NO_ED25519
TestKexDhReplyRejectsEd25519CorruptSig();
#endif
TestKexDhReplyRejectsSigNameOverrun();
#endif

#ifdef WOLFSSH_SFTP
Expand Down
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