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fix(sip): raise header value cap to 4 KB for carrier tokens like X-Twilio-CallToken #1750

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fix(sip): raise header value cap to 4 KB for carrier tokens like X-Twilio-CallToken #1750

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6 changes: 6 additions & 0 deletions .changeset/sip-header-value-cap.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
"github.com/livekit/protocol": patch
"@livekit/protocol": patch
---

Raise the SIP header value cap from 1 KB to 4 KB so carrier headers like Twilio's `X-Twilio-CallToken` (Immutable Call Forwarding token with SHAKEN/STIR PASSporTs, >1 KB) pass `CreateSIPParticipant` validation
15 changes: 13 additions & 2 deletions livekit/sip_validation.go
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Expand Up @@ -149,6 +149,12 @@ func init() {
headerValuesCharacters.AddUTF8()
}

// maxHeaderValueLength caps a single SIP header value. It is not an RFC limit
// (RFC 3261 §7.1 bounds the message, not headers), but guards against abusive
// or oversized values. Set above carriers' real-world maximums — Twilio's
// X-Twilio-CallToken exceeds 1 KB — and well below the 8 KB UDP datagram bound.
const maxHeaderValueLength = 4096

// Required headers for SIP requests per RFC 3261 Section 8.1.1
var RequiredRequestHeaders = map[string]bool{
"via": true,
Expand Down Expand Up @@ -257,8 +263,13 @@ func ValidateHeaderValueResult(name, value string) ValidationResult {
return ValidationResult{}
}

if len(value) > 1024 {
return ValidationFailure(fmt.Errorf("header %s: value too long (max 1024 characters)", name))
// RFC 3261 caps the whole message (8 KB per §7.1 when UDP), not individual
// header values. Carriers do exceed 1 KB on a single header — e.g. Twilio's
// X-Twilio-CallToken carries an Immutable Call Forwarding token with
// SHAKEN/STIR + DIV PASSporTs that must be forwarded unchanged. 4096 keeps
// a single header from dominating a datagram while tolerating those.
if len(value) > maxHeaderValueLength {
return ValidationFailure(fmt.Errorf("header %s: value too long (max %d characters)", name, maxHeaderValueLength))
}

// Basic character validation - printable ASCII. We're stricter than the spec here - no UTF-8 for now
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5 changes: 3 additions & 2 deletions livekit/sip_validation_test.go
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Expand Up @@ -99,7 +99,8 @@ var ValidHeaderValues = []string{
"Header with unicode café", // Unicode
"Header with unicode 世界", // Unicode
"Header with unicode émojis 🎉", // Unicode with emojis
strings.Repeat("a", 1024), // max length
strings.Repeat("a", 1024), // beyond carrier needs (e.g. X-Twilio-CallToken)
strings.Repeat("a", 4096), // max length
}

// Note: These restrictions are NOT in RFC 3261 but are applied for security/performance
Expand All @@ -110,7 +111,7 @@ var InvalidHeaderValues = []string{
"Header with\x01control", // control character
"Header with\x1Funit separator", // control character
"Header with\x7Fdelete", // delete character
strings.Repeat("a", 1025), // too long
strings.Repeat("a", 4097), // too long
}

// testCaseName truncates a test case name to maxLen and adds dots with total size
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