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wolfsshd: fix peer-controlled over-read in Windows pseudo-console resize #1005

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wolfsshd: fix peer-controlled over-read in Windows pseudo-console resize #1005

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wolfsshd: fix peer-controlled over-read in Windows pseudo-console resize
yosuke-wolfssl Jun 8, 2026
6756ff5
Fix
yosuke-wolfssl Jun 8, 2026
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17 changes: 13 additions & 4 deletions apps/wolfsshd/wolfsshd.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1002,17 +1002,26 @@ static int SHELL_Subsystem(WOLFSSHD_CONNECTION* conn, WOLFSSH* ssh,
}

if (ret == WS_SUCCESS) {
char cmdWSize[20];
int cmdWSizeSz = 20;
/* Worst case "\x1b[8;%u;%ut" with two 10-digit word32 values is 26
* bytes plus the terminator; size generously. */
char cmdWSize[32];
int cmdWSizeSz;
DWORD wrtn = 0;

wolfSSH_Log(WS_LOG_INFO, "[SSHD] Successfully created process for "
"console, waiting for it to start");

WaitForInputIdle(processInfo.hProcess, 1000);

/* Send initial terminal size to pseudo console with VT control sequence */
cmdWSizeSz = snprintf(cmdWSize, cmdWSizeSz, "\x1b[8;%d;%dt", ssh->heightRows, ssh->widthChar);
/* Send initial terminal size to pseudo console with VT control sequence.
* heightRows/widthChar are peer-supplied word32 values, so format them
* with %u and clamp the return value before handing it to WriteFile to
* avoid over-reading the stack buffer. */
cmdWSizeSz = WSNPRINTF(cmdWSize, sizeof(cmdWSize), "\x1b[8;%u;%ut",
ssh->heightRows, ssh->widthChar);
if (cmdWSizeSz < 0 || cmdWSizeSz >= (int)sizeof(cmdWSize)) {
cmdWSizeSz = (int)sizeof(cmdWSize) - 1;
}
if (WriteFile(ptyIn, cmdWSize, cmdWSizeSz, &wrtn, 0) != TRUE) {
WLOG(WS_LOG_ERROR, "Issue with pseudo console resize");
ret = WS_FATAL_ERROR;
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