util.xml: Do not allow doctypes, comments or processing instructions
Yes. This is as bad as it sounds. CVE pending.
In Prosody itself, this only affects mod_websocket, which uses util.xml
to parse the <open/> frame, thus allowing unauthenticated remote DoS
using Billion Laughs. However, third-party modules using util.xml may
also be affected by this.
This commit installs handlers which disallow the use of doctype
declarations and processing instructions without any escape hatch. It,
by default, also introduces such a handler for comments, however, there
is a way to enable comments nontheless.
This is because util.xml is used to parse human-facing data, where
comments are generally a desirable feature, and also because comments
are generally harmless.
Should pass: 41 42 43 # Simple ASCII - abc
Should pass: 41 42 c3 87 # "ABÇ"
Should pass: 41 42 e1 b8 88 # "ABḈ"
Should pass: 41 42 f0 9d 9c 8d # "AB𝜍"
Should pass: F4 8F BF BF # Last valid sequence (U+10FFFF)
Should fail: F4 90 80 80 # First invalid sequence (U+110000)
Should fail: 80 81 82 83 # Invalid sequence (invalid start byte)
Should fail: C2 C3 # Invalid sequence (invalid continuation byte)
Should fail: C0 43 # Overlong sequence
Should fail: F5 80 80 80 # U+140000 (out of range)
Should fail: ED A0 80 # U+D800 (forbidden by RFC 3629)
Should fail: ED BF BF # U+DFFF (forbidden by RFC 3629)
Should pass: ED 9F BF # U+D7FF (U+D800 minus 1: allowed)
Should pass: EE 80 80 # U+E000 (U+D7FF plus 1: allowed)
Should fail: C0 # Invalid start byte
Should fail: C1 # Invalid start byte
Should fail: C2 # Incomplete sequence
Should fail: F8 88 80 80 80 # 6-byte sequence
Should pass: 7F # Last valid 1-byte sequence (U+00007F)
Should pass: DF BF # Last valid 2-byte sequence (U+0007FF)
Should pass: EF BF BF # Last valid 3-byte sequence (U+00FFFF)
Should pass: 00 # First valid 1-byte sequence (U+000000)
Should pass: C2 80 # First valid 2-byte sequence (U+000080)
Should pass: E0 A0 80 # First valid 3-byte sequence (U+000800)
Should pass: F0 90 80 80 # First valid 4-byte sequence (U+000800)
Should fail: F8 88 80 80 80 # First 5-byte sequence - invalid per RFC 3629
Should fail: FC 84 80 80 80 80 # First 6-byte sequence - invalid per RFC 3629
Should pass: EF BF BD # U+00FFFD (replacement character)
Should fail: 80 # First continuation byte
Should fail: BF # Last continuation byte
Should fail: 80 BF # 2 continuation bytes
Should fail: 80 BF 80 # 3 continuation bytes
Should fail: 80 BF 80 BF # 4 continuation bytes
Should fail: 80 BF 80 BF 80 # 5 continuation bytes
Should fail: 80 BF 80 BF 80 BF # 6 continuation bytes
Should fail: 80 BF 80 BF 80 BF 80 # 7 continuation bytes
Should fail: FE # Impossible byte
Should fail: FF # Impossible byte
Should fail: FE FE FF FF # Impossible bytes
Should fail: C0 AF # Overlong "/"
Should fail: E0 80 AF # Overlong "/"
Should fail: F0 80 80 AF # Overlong "/"
Should fail: F8 80 80 80 AF # Overlong "/"
Should fail: FC 80 80 80 80 AF # Overlong "/"
Should fail: C0 80 AF # Overlong "/" (invalid)
Should fail: C1 BF # Overlong
Should fail: E0 9F BF # Overlong
Should fail: F0 8F BF BF # Overlong
Should fail: F8 87 BF BF BF # Overlong
Should fail: FC 83 BF BF BF BF # Overlong
Should pass: EF BF BE # U+FFFE (invalid unicode, valid UTF-8)
Should pass: EF BF BF # U+FFFF (invalid unicode, valid UTF-8)