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7.6

wolfSSH may crash from crafted SFTP path

CVE-2026-83742 · published 29 days ago
Summary

The wolfSSH component used for SFTP on non-Windows systems can write a single stray null byte past the end of a memory buffer when it processes a specially crafted file path. This may corrupt nearby data and cause the application to stop working. Update wolfSSH to the latest version or ensure that path buffers are large enough to hold the full input.

What to do
  • Update wolfssl inc. wolfssh to version 1.6.0.
  • Update wolfssh wolfssh to version 1.6.0 or later.
Affected software
VendorProductAffected versions
wolfssl inc. wolfssh <= 1.5.0
Fix: upgrade to 1.6.0
wolfssh wolfssh >= 1.4.11, < 1.6.0
cpe:2.3:a:wolfssh:wolfssh:*:*:*:*:*:*:*:*
Original advisory text
wstrncat() unsigned integer underflow leads to an off-by-one null write in wolfSSH on non-Windows platforms
Unsigned integer underflow in wstrncat() in src/port.c in wolfSSL wolfSSH from v1.4.11 through v1.5.0 on non-Windows platforms allows an authenticated remote attacker to write one out-of-bounds null byte past the end of a stack buffer by sending a crafted SFTP path. wolfSSH_RealPath() in src/ssh.c appends each path component with a remaining-size bound (outSz - curSz) rather than the full destination size, so once the accumulated path reaches half the output buffer the size_t computation n - strlen(s1) - 1 wraps to near SIZE_MAX. The strncat() call is then effectively unbounded and copies the whole component; when that component exactly fills the remainder of the buffer, its terminating null is written one byte past the end. The caller's own length check keeps the copied data inside the buffer, so the overflow is limited to that single null byte, which may corrupt an adjacent stack value and crash the process. Applications that call the public wolfSSH_RealPath() with an output buffer smaller than the input path are additionally exposed to an unbounded copy, because the word32 expression outSz - segSz in that length check also wraps.
References
Fix within
Internet-facing 60 days
Internal At next upgrade
  • Not known to be exploited
  • Needs hands-on effort to exploit
  • Gives an attacker partial control
Severity
7.6 High
Exploitation
<1% chance of attack within 30 days
Type
CWE-121Stack-based Buffer Overflow
CWE-191Integer Underflow (Wrap or Wraparound)
CWE-193Off-by-one Error
Timeline
Published7 Oct 2026
Updated4 Nov 2026
First seen7 Oct 2026
Sources
CVE-2026-83742 · NVD
CVE-2026-83742 · MITRE
CVE-2026-83742 · OSV
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