Custom oid in eku

[anhu]

Note

Medium Risk
Touches X.509 EKU parsing, which can affect certificate acceptance/rejection paths; behavior remains unchanged unless WC_ASN_UNKNOWN_EXT_CB is enabled and a callback is registered.

Overview
Adds a new public API, wc_SetUnknownExtKeyUsageCallback, allowing applications to decide whether unknown Extended Key Usage OIDs encountered during certificate parsing should be accepted or rejected.

Wires this callback through DecodedCert into DecodeExtKeyUsage (signature extended), invoking it when EKU OIDs are unrecognized (including cases where the OID parses but doesn’t map to known EKU bits). Updates OpenSSL-compat codepaths to pass NULL for the new parameter and documents the new callback in asn_public.h.

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[anhu]

@aisle-analyzer

[anhu]

@aisle-analyzer , does this comment make sense?

[cursor]

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[cursor]

Buffer size passed as bytes instead of elements

Medium Severity

decOidSz is initialized to sizeof(decOid) which yields the byte size (MAX_OID_SZ * sizeof(word16) = 64), but DecodeObjectId interprets *outSz as the number of elements in the array (documented as "On in, number of elements in array"). The decOid array only holds MAX_OID_SZ (32) elements. The bounds check inside DecodeObjectId (y >= (int)*outSz) would allow writing up to index 63, causing a stack buffer overflow for OIDs with more than ~31 dotted components. The correct value is MAX_OID_SZ or sizeof(decOid)/sizeof(decOid[0]). This follows a pre-existing pattern elsewhere in the file, but each new call site is a new exploitable path reachable via a crafted certificate.

Additional Locations (2)

• wolfcrypt/src/asn.c#L22220-L22221
• wolfcrypt/src/asn.c#L22275-L22276