GNU libidn2 before 2.2.0 fails to perform the roundtrip checks specified in RFC3490 Section 4.2 when converting A-labels to U-labels. This makes it possible in some circumstances for one domain to impersonate another. By creating a malicious domain that matches a target domain except for the inclusion of certain punycoded Unicode characters (that would be discarded when converted first to a Unicode label and then back to an ASCII label), arbitrary domains can be impersonated.

idn2_to_ascii_4i in lib/lookup.c in GNU libidn2 before 2.1.1 has a heap-based buffer overflow via a long domain string.

Integer overflow in the _isBidi function in bidi.c in Libidn2 before 2.0.4 allows remote attackers to cause a denial of service or possibly have unspecified other impact.

Integer overflow in the decode_digit function in puny_decode.c in Libidn2 before 2.0.4 allows remote attackers to cause a denial of service or possibly have unspecified other impact.

The stringprep_utf8_nfkc_normalize function in lib/nfkc.c in libidn before 1.33 allows context-dependent attackers to cause a denial of service (out-of-bounds read and crash) via crafted UTF-8 data.

idn in GNU libidn before 1.33 might allow remote attackers to obtain sensitive memory information by reading a zero byte as input, which triggers an out-of-bounds read.

The idna_to_ascii_4i function in lib/idna.c in libidn before 1.33 allows context-dependent attackers to cause a denial of service (out-of-bounds read and crash) via 64 bytes of input.

idn in libidn before 1.33 might allow remote attackers to obtain sensitive memory information by reading a zero byte as input, which triggers an out-of-bounds read, a different vulnerability than CVE-2015-8948.

The stringprep_utf8_to_ucs4 function in libin before 1.31, as used in jabberd2, allows context-dependent attackers to read system memory and possibly have other unspecified impact via invalid UTF-8 characters in a string, which triggers an out-of-bounds read.