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fix: prevent indefinite hangs during TLS operations (#819) #955

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CharlesWong wants to merge 7 commits into from
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fix: prevent indefinite hangs during TLS operations (#819) #955

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136bedb
chore(deps): bump golang.org/x/crypto from 0.38.0 to 0.45.0
dependabot[bot] Nov 20, 2025
d13b67f
Merge pull request #875 from projectdiscovery/dependabot/go_modules/g…
dogancanbakir Jan 6, 2026
1b1c047
fix: prevent indefinite hangs during TLS operations (#819)
CharlesWong Mar 10, 2026
fd2b535
fix: handle zero timeout to avoid already-expired context
CharlesWong Mar 10, 2026
57d4d61
fix: use idiomatic if Timeout>0 guard for cipher enum contexts
CharlesWong Mar 11, 2026
b936f57
refactor: fix ctx parameter order and stale comment in ztls
CharlesWong Mar 11, 2026
7194d08
fix(ztls): prefer completed handshake over simultaneous timeout
CharlesWong Mar 11, 2026
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16 changes: 8 additions & 8 deletions go.mod
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -92,8 +92,8 @@ require (
github.com/zcalusic/sysinfo v1.0.2 // indirect
go4.org v0.0.0-20230225012048-214862532bf5 // indirect
golang.org/x/oauth2 v0.28.0 // indirect
golang.org/x/sync v0.14.0 // indirect
golang.org/x/term v0.32.0 // indirect
golang.org/x/sync v0.18.0 // indirect
golang.org/x/term v0.37.0 // indirect
)

require (
Expand Down Expand Up @@ -125,12 +125,12 @@ require (
github.com/weppos/publicsuffix-go v0.40.3-0.20250408071509-6074bbe7fd39 // indirect
github.com/zmap/rc2 v0.0.0-20190804163417-abaa70531248 // indirect
go.etcd.io/bbolt v1.4.0 // indirect
golang.org/x/crypto v0.38.0 // indirect
golang.org/x/mod v0.24.0 // indirect
golang.org/x/net v0.40.0
golang.org/x/sys v0.33.0 // indirect
golang.org/x/text v0.25.0 // indirect
golang.org/x/tools v0.31.0 // indirect
golang.org/x/crypto v0.45.0 // indirect
golang.org/x/mod v0.29.0 // indirect
golang.org/x/net v0.47.0
golang.org/x/sys v0.38.0 // indirect
golang.org/x/text v0.31.0 // indirect
golang.org/x/tools v0.38.0 // indirect
google.golang.org/protobuf v1.36.6 // indirect
gopkg.in/djherbis/times.v1 v1.3.0 // indirect
gopkg.in/yaml.v3 v3.0.1 // indirect
Expand Down
32 changes: 16 additions & 16 deletions go.sum
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -414,8 +414,8 @@ golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5y
golang.org/x/crypto v0.0.0-20211209193657-4570a0811e8b/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
golang.org/x/crypto v0.7.0/go.mod h1:pYwdfH91IfpZVANVyUOhSIPZaFoJGxTFbZhFTx+dXZU=
golang.org/x/crypto v0.11.0/go.mod h1:xgJhtzW8F9jGdVFWZESrid1U1bjeNy4zgy5cRr/CIio=
golang.org/x/crypto v0.38.0 h1:jt+WWG8IZlBnVbomuhg2Mdq0+BBQaHbtqHEFEigjUV8=
golang.org/x/crypto v0.38.0/go.mod h1:MvrbAqul58NNYPKnOra203SB9vpuZW0e+RRZV+Ggqjw=
golang.org/x/crypto v0.45.0 h1:jMBrvKuj23MTlT0bQEOBcAE0mjg8mK9RXFhRH6nyF3Q=
golang.org/x/crypto v0.45.0/go.mod h1:XTGrrkGJve7CYK7J8PEww4aY7gM3qMCElcJQ8n8JdX4=
golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
golang.org/x/exp v0.0.0-20190510132918-efd6b22b2522/go.mod h1:ZjyILWgesfNpC6sMxTJOJm9Kp84zZh5NQWvqDGG3Qr8=
Expand Down Expand Up @@ -445,8 +445,8 @@ golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzB
golang.org/x/mod v0.2.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
golang.org/x/mod v0.6.0-dev.0.20220419223038-86c51ed26bb4/go.mod h1:jJ57K6gSWd91VN4djpZkiMVwK6gcyfeH4XE8wZrZaV4=
golang.org/x/mod v0.8.0/go.mod h1:iBbtSCu2XBx23ZKBPSOrRkjjQPZFPuis4dIYUhu/chs=
golang.org/x/mod v0.24.0 h1:ZfthKaKaT4NrhGVZHO1/WDTwGES4De8KtWO0SIbNJMU=
golang.org/x/mod v0.24.0/go.mod h1:IXM97Txy2VM4PJ3gI61r1YEk/gAj6zAHN3AdZt6S9Ww=
golang.org/x/mod v0.29.0 h1:HV8lRxZC4l2cr3Zq1LvtOsi/ThTgWnUk/y64QSs8GwA=
golang.org/x/mod v0.29.0/go.mod h1:NyhrlYXJ2H4eJiRy/WDBO6HMqZQ6q9nk4JzS3NuCK+w=
golang.org/x/net v0.0.0-20180724234803-3673e40ba225/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
golang.org/x/net v0.0.0-20180826012351-8a410e7b638d/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
Expand Down Expand Up @@ -474,8 +474,8 @@ golang.org/x/net v0.7.0/go.mod h1:2Tu9+aMcznHK/AK1HMvgo6xiTLG5rD5rZLDS+rp2Bjs=
golang.org/x/net v0.8.0/go.mod h1:QVkue5JL9kW//ek3r6jTKnTFis1tRmNAW2P1shuFdJc=
golang.org/x/net v0.10.0/go.mod h1:0qNGK6F8kojg2nk9dLZ2mShWaEBan6FAoqfSigmmuDg=
golang.org/x/net v0.12.0/go.mod h1:zEVYFnQC7m/vmpQFELhcD1EWkZlX69l4oqgmer6hfKA=
golang.org/x/net v0.40.0 h1:79Xs7wF06Gbdcg4kdCCIQArK11Z1hr5POQ6+fIYHNuY=
golang.org/x/net v0.40.0/go.mod h1:y0hY0exeL2Pku80/zKK7tpntoX23cqL3Oa6njdgRtds=
golang.org/x/net v0.47.0 h1:Mx+4dIFzqraBXUugkia1OOvlD6LemFo1ALMHjrXDOhY=
golang.org/x/net v0.47.0/go.mod h1:/jNxtkgq5yWUGYkaZGqo27cfGZ1c5Nen03aYrrKpVRU=
golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
Expand All @@ -493,8 +493,8 @@ golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJ
golang.org/x/sync v0.0.0-20200317015054-43a5402ce75a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.0.0-20220722155255-886fb9371eb4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.1.0/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
golang.org/x/sync v0.14.0 h1:woo0S4Yywslg6hp4eUFjTVOyKt0RookbpAHG4c1HmhQ=
golang.org/x/sync v0.14.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
golang.org/x/sync v0.18.0 h1:kr88TuHDroi+UVf+0hZnirlk8o8T+4MrK6mr60WkH/I=
golang.org/x/sync v0.18.0/go.mod h1:9KTHXmSnoGruLpwFjVSX0lNNA75CykiMECbovNTZqGI=
golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
golang.org/x/sys v0.0.0-20180909124046-d0be0721c37e/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
Expand Down Expand Up @@ -531,17 +531,17 @@ golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.11.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.33.0 h1:q3i8TbbEz+JRD9ywIRlyRAQbM0qF7hu24q3teo2hbuw=
golang.org/x/sys v0.33.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
golang.org/x/sys v0.38.0 h1:3yZWxaJjBmCWXqhN1qh02AkOnCQ1poK6oF+a7xWL6Gc=
golang.org/x/sys v0.38.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=
golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
golang.org/x/term v0.5.0/go.mod h1:jMB1sMXY+tzblOD4FWmEbocvup2/aLOaQEp7JmGp78k=
golang.org/x/term v0.6.0/go.mod h1:m6U89DPEgQRMq3DNkDClhWw02AUbt2daBVO4cn4Hv9U=
golang.org/x/term v0.8.0/go.mod h1:xPskH00ivmX89bAKVGSKKtLOWNx2+17Eiy94tnKShWo=
golang.org/x/term v0.10.0/go.mod h1:lpqdcUyK/oCiQxvxVrppt5ggO2KCZ5QblwqPnfZ6d5o=
golang.org/x/term v0.32.0 h1:DR4lr0TjUs3epypdhTOkMmuF5CDFJ/8pOnbzMZPQ7bg=
golang.org/x/term v0.32.0/go.mod h1:uZG1FhGx848Sqfsq4/DlJr3xGGsYMu/L5GW4abiaEPQ=
golang.org/x/term v0.37.0 h1:8EGAD0qCmHYZg6J17DvsMy9/wJ7/D/4pV/wfnld5lTU=
golang.org/x/term v0.37.0/go.mod h1:5pB4lxRNYYVZuTLmy8oR2BH8dflOR+IbTYFD8fi3254=
golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
Expand All @@ -554,8 +554,8 @@ golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=
golang.org/x/text v0.8.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
golang.org/x/text v0.9.0/go.mod h1:e1OnstbJyHTd6l/uOt8jFFHp6TRDWZR/bV3emEE/zU8=
golang.org/x/text v0.11.0/go.mod h1:TvPlkZtksWOMsz7fbANvkp4WM8x/WCo/om8BMLbz+aE=
golang.org/x/text v0.25.0 h1:qVyWApTSYLk/drJRO5mDlNYskwQznZmkpV2c8q9zls4=
golang.org/x/text v0.25.0/go.mod h1:WEdwpYrmk1qmdHvhkSTNPm3app7v4rsT8F2UD6+VHIA=
golang.org/x/text v0.31.0 h1:aC8ghyu4JhP8VojJ2lEHBnochRno1sgL6nEi9WGFGMM=
golang.org/x/text v0.31.0/go.mod h1:tKRAlv61yKIjGGHX/4tP1LTbc13YSec1pxVEWXzfoeM=
golang.org/x/time v0.0.0-20181108054448-85acf8d2951c/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
golang.org/x/time v0.0.0-20190308202827-9d24e82272b4/go.mod h1:tRJNPiyCQ0inRvYxbN9jk5I+vvW/OXSQhTDSoE431IQ=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
Expand Down Expand Up @@ -585,8 +585,8 @@ golang.org/x/tools v0.0.0-20200207183749-b753a1ba74fa/go.mod h1:TB2adYChydJhpapK
golang.org/x/tools v0.0.0-20200212150539-ea181f53ac56/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
golang.org/x/tools v0.1.12/go.mod h1:hNGJHUnrk76NpqgfD5Aqm5Crs+Hm0VOH/i9J2+nxYbc=
golang.org/x/tools v0.6.0/go.mod h1:Xwgl3UAJ/d3gWutnCtw505GrjyAbvKui8lOU390QaIU=
golang.org/x/tools v0.31.0 h1:0EedkvKDbh+qistFTd0Bcwe/YLh4vHwWEkiI0toFIBU=
golang.org/x/tools v0.31.0/go.mod h1:naFTU+Cev749tSJRXJlna0T3WxKvb1kWEx15xA4SdmQ=
golang.org/x/tools v0.38.0 h1:Hx2Xv8hISq8Lm16jvBZ2VQf+RLmbd7wVUsALibYI/IQ=
golang.org/x/tools v0.38.0/go.mod h1:yEsQ/d/YK8cjh0L6rZlY8tgtlKiBNTL14pGDJPJpYQs=
golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
Expand Down
11 changes: 10 additions & 1 deletion pkg/tlsx/tls/tls.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -236,10 +236,19 @@ func (c *Client) EnumerateCiphers(hostname, ip, port string, options clients.Con

conn := tls.Client(baseConn, baseCfg)

if err := conn.Handshake(); err == nil {
// Use HandshakeContext with timeout to prevent indefinite hangs (#819).
// Mirror the zero-timeout guard from the main connect path (lines 109-114):
// when Timeout is unset (0), use a plain Background context (no expiry).
handshakeCtx := context.Background()
cancel := func() {}
if c.options.Timeout > 0 {
handshakeCtx, cancel = context.WithTimeout(handshakeCtx, time.Duration(c.options.Timeout)*time.Second)
}
if err := conn.HandshakeContext(handshakeCtx); err == nil {
ciphersuite := conn.ConnectionState().CipherSuite
enumeratedCiphers = append(enumeratedCiphers, tls.CipherSuiteName(ciphersuite))
}
cancel()
_ = conn.Close() // close baseConn internally
}
return enumeratedCiphers, nil
Expand Down
59 changes: 47 additions & 12 deletions pkg/tlsx/ztls/ztls.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,7 @@ func (c *Client) ConnectWithOptions(hostname, ip, port string, options clients.C

// new tls connection
tlsConn := tls.Client(conn, config)
err = c.tlsHandshakeWithTimeout(tlsConn, ctx)
err = c.tlsHandshakeWithTimeout(ctx, tlsConn)
if err != nil {
if clients.IsClientCertRequiredError(err) {
clientCertRequired = true
Expand Down Expand Up @@ -257,10 +257,19 @@ func (c *Client) EnumerateCiphers(hostname, ip, port string, options clients.Con
conn := tls.Client(baseConn, baseCfg)
baseCfg.CipherSuites = []uint16{ztlsCiphers[v]}

if err := c.tlsHandshakeWithTimeout(conn, context.TODO()); err == nil {
// Use a timeout context for each cipher handshake to prevent indefinite hangs (#819).
// Mirror the zero-timeout guard at lines 118-122: when Timeout is unset (0),
// use a plain Background context (no expiry) rather than an already-expired one.
handshakeCtx := context.Background()
cancel := func() {}
if c.options.Timeout > 0 {
handshakeCtx, cancel = context.WithTimeout(handshakeCtx, time.Duration(c.options.Timeout)*time.Second)
}
if err := c.tlsHandshakeWithTimeout(handshakeCtx, conn); err == nil {
h1 := conn.GetHandshakeLog()
enumeratedCiphers = append(enumeratedCiphers, h1.ServerHello.CipherSuite.String())
}
cancel()
_ = conn.Close() // also closes baseConn internally
}
return enumeratedCiphers, nil
Expand Down Expand Up @@ -320,20 +329,46 @@ func (c *Client) getConfig(hostname, ip, port string, options clients.ConnectOpt
return config, nil
}

// tlsHandshakeWithCtx attempts tls handshake with given timeout
func (c *Client) tlsHandshakeWithTimeout(tlsConn *tls.Conn, ctx context.Context) error {
// tlsHandshakeWithTimeout attempts tls handshake with given timeout.
//
// Previous implementation had a critical bug: it used
// case errChan <- tlsConn.Handshake():
// which evaluates Handshake() synchronously before the send, making the
// ctx.Done() branch unreachable — the select could never cancel a stuck
// handshake (#819).
//
// Fixed by running Handshake() in a goroutine and closing the connection
// on timeout to unblock it.
//
// Note on select fairness: when both errChan and ctx.Done() are ready
// simultaneously, Go's select chooses randomly. We prefer a completed
// handshake result over a timeout by checking errChan non-blockingly
// in the ctx.Done() branch before returning the timeout error.
func (c *Client) tlsHandshakeWithTimeout(ctx context.Context, tlsConn *tls.Conn) error {
errChan := make(chan error, 1)
defer close(errChan)
go func() {
errChan <- tlsConn.Handshake()
}()

select {
case err := <-errChan:
if err == tls.ErrCertsOnly {
err = nil
}
return err
case <-ctx.Done():
// Prefer a completed handshake result that arrived at the same time
// as the deadline — select is non-deterministic when both are ready.
select {
case err := <-errChan:
if err == tls.ErrCertsOnly {
err = nil
}
return err
default:
}
// Close the connection to unblock the goroutine stuck in Handshake()
_ = tlsConn.Close()
return errorutil.NewWithTag("ztls", "timeout while attempting handshake") //nolint
case errChan <- tlsConn.Handshake():
}

err := <-errChan
if err == tls.ErrCertsOnly {
err = nil
}
return err
}