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Harden third-party dependency boundaries - #71
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- Go toolchain & build hygiene:
- Update go/go.mod to go 1.27.3 to match .goversion and export GOTOOLCHAIN in go/build.sh.
- Exclude stale xterm.js from sshterm-server's embedded docroot.
- Centralized third-party dependency workarounds (go/internal/depfix):
- Add feature-flagged workarounds and depfix.WithDisabled helper so each vulnerability and its remediation can be verified in dual-mode tests and cleanly removed once fixed upstream.
- github.com/pkg/sftp (EnableSFTPPacketGuard, EnableSFTPPathAndRemoveGuard, EnableSFTPResourceGuard):
- Interpose sftpSafeConn via sftp.NewClientPipe to bounds-check incoming SFTP packets (SSH_FXP_VERSION, SSH_FXP_STATUS, SSH_FXP_HANDLE, SSH_FXP_DATA, SSH_FXP_NAME, SSH_FXP_ATTRS) before pkg/sftp unmarshals them with unchecked slice bounds.
- Reject 0-byte SSH_FXP_DATA responses that trigger an infinite read loop in File.readChunkAt, cap cumulative SSH_FXP_READDIR entries, and reject READDIR filenames containing '/' or resolving to '.' / '..'.
- Provide Lstat-based depfix.RemoveAll so recursive removal does not follow directory symlinks, and wrap JS callback boundaries in jsutil.TryCatch.
- golang.org/x/crypto/ssh & ssh/agent (EnableSSHAgentGuard, EnableRSASHA2, EnableSSHSessionExitGuard, EnableCertSignatureGuard):
- Bound concurrent forwarded agent channels, cap incoming agent request frames to 256 KiB before agent.ServeAgent pre-allocates up to 16 MiB, and reject non-list/sign agent message types before ServeAgent parses attacker-supplied keys.
- Implement ssh.MultiAlgorithmSigner on dynSigner and agent.ExtendedAgent on keyRing and forwardedAgent so RSA keys and certificates use rsa-sha2-256 / rsa-sha2-512 instead of falling back to SHA-1 (ssh-rsa).
- Wrap SSH session channels so malformed exit-status or exit-signal requests close the channel and drain remaining requests instead of deadlocking (*ssh.Session).Wait and mux.loop.
- Reject deprecated SHA-1 (ssh-rsa) and DSA (ssh-dss) CA signatures in certificate verification and support no-touch-required (Flags=0) sk-* CA signatures.
- golang.org/x/term (EnableTermEscapeGuard):
- Terminate runaway (>64-byte) unterminated escape sequences in WrapTermReadWriter before Terminal.inBuf ([256]byte) fills up and spins in a synchronous 0-byte Read loop.
- Document the removal procedure and residual risks in go/internal/depfix/README.md.
- Frontend @xterm/xterm workarounds & terminal hardening (docroot/ssh.mjs, go/internal/terminal):
- Add window.sshApp.workarounds (csiRepGuard, csiLoopGuard, oscQueryAndLinkGuard) and applyXtermWorkarounds to clamp CSI Ps b (preventing RangeError in repeatPrecedingCharacter from wedging WriteBuffer) and CSI I/Z/L/M/S/T loop counts, and to rate-limit chained OSC 4 color queries and OSC 8 hyperlink markers.
- Sanitize and cap OSC 0 / OSC 2 window titles and reuse a single toast element in TabManager._showMessage.
- Reset terminal session modes and drain pending onData responses between SSH/SFTP sessions via Terminal.ResetSessionState.
- Local fixes:
- Fix duplicate trailing backslash append to bufRaw in go/internal/shellwords.Parse that could cause an out-of-bounds slice panic during tab completion.
- Set HandshakeTimeout on the WebSocket upgrader and per-write deadlines on upstream TCP connections in sshterm-server.
- Update CHANGELOG.md.
rthellend
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rthellend
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October 25, 2026 15:36
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Summary
This PR upgrades
github.com/pkg/sftptov1.13.12, adds RSA SHA-2 signing support for user certificates and forwarded agents, rejects deprecated SHA-1/DSA CA signatures, and hardenssshtermandsshterm-serveragainst terminal, auto-completion, and proxy edge cases.Changes
1. SFTP Client (
github.com/pkg/sftpv1.13.12)github.com/pkg/sftptov1.13.12: Fixes upstream slice bounds panics on truncated/malformed server packets andClient.RemoveAlldirectory symlink traversal.2. SSH Client, Certificates, & Forwarded Agent (
golang.org/x/crypto/ssh)rsa-sha2-256/rsa-sha2-512) Support:ssh.MultiAlgorithmSignerondynSignerso RSA keys and RSA-backed user certificates advertise and sign withrsa-sha2-512andrsa-sha2-256.agent.ExtendedAgent(SignWithFlags) onkeyRingandforwardedAgentso remote hosts requesting SHA-2 signatures viaSSH_AGENTC_SIGN_REQUESTflags receiversa-sha2-256/rsa-sha2-512instead of falling back to SHA-1 (ssh-rsa).ssh-rsa(SHA-1) andssh-dss(DSA) CA signatures incheckCertificate.3. Tab Auto-Completion & Standalone Server (
internal/shellwords,sshterm-server,go/build.sh)shellwords.Parseso a trailing unquoted\keepsrawandargsaligned instead of panicking with an out-of-bounds slice during tab auto-completion.go/go.mod(go 1.27.3) andgo/build.sh(GOTOOLCHAIN) with.goversionso local builds do not fall back to an older host toolchain, and strips staledocroot/xterm.jsfrom the embedded server docroot.HandshakeTimeout: 10 * time.Secondonwebsocket.Upgraderand applies a write deadline (tcpDeadlineWriter) on upstream TCP writes inproxyConn.4. Frontend Terminal Hardening (
@xterm/xtermindocroot/ssh.mjs)csiRepGuard: InterceptsCSI Ps b(REP) and clampsPstoterm.cols, preventingString.prototype.repeat(2147483647)from throwing an uncaughtRangeErrorthat wedgesWriteBufferand deadlocks WASMTerminal.Write.csiLoopGuard: Clamps parameters onCSI I(CHT),CSI Z(CBT),CSI L(IL),CSI M(DL),CSI S(SU), andCSI T(SD) to terminal dimensions to prevent2^31 - 1synchronous main-thread loops.OSC 0/OSC 2titles to 128 characters while reusing a single.sshterm-toastDOM node per screen, and resets terminal modes and pending input buffers (ResetSessionState) when an SSH or SFTP session ends.Verification
go/internal/shellwords/...,go/internal/app/..., andgo/sshterm-server/...go/internal/tests/remediations_test.go