[High] Date/time review truncates multi-byte uint values in ui_712_format_datetime

[donjon-cerberus-sandbox]

Location

• File: src/features/sign_message_eip712/ui_logic.c
• Lines: 708-719

Classification

Property	Value
Severity	High
Category	Other
CWE	CWE-CWE-451
OWASP	A04:2021-Insecure Design
Confidence	Confirmed
Likelihood	Medium

Technical Description

The date/time formatter accepts any uint field selected by a trusted date-time filter, but it converts the raw value with u64_from_BE(data, length). u64_from_BE() only consumes the first 8 bytes of the supplied buffer. For EIP-712 uint256 timestamps, or for non-minimal encodings with attacker-added leading zero bytes, the device displays a truncated/smaller timestamp while the signing hash is computed from the full integer value. Because leading zero bytes do not change the final 32-byte EIP-712 integer encoding, a malicious host can keep the signed value valid while showing a much earlier date on-screen.

Vulnerable Code

static bool ui_712_format_datetime(const uint8_t *data,
                                   uint8_t length,
                                   const s_struct_712_field *field_ptr) {
    time_t timestamp;

    if ((length >= field_ptr->type_size) && ismaxint((uint8_t *) data, length)) {
        snprintf(strings.tmp.tmp, sizeof(strings.tmp.tmp), "Unlimited");
        return true;
    }
    timestamp = u64_from_BE(data, length);
    return time_format_to_utc(&timestamp, strings.tmp.tmp, sizeof(strings.tmp.tmp));
}

Impact

Network: a remote wallet-connected attacker can craft EIP-712 timestamp/deadline fields so the review screen shows an earlier or expired-looking date while the signed message contains a longer-lived deadline. This can trick the user into approving signatures that remain valid far longer than displayed.

Remediation

Only allow date/time formatting for integers that fit within 64 bits, and reject non-minimal encodings. Alternatively, normalize the value first by stripping leading zeros and then require the remaining length to be <= 8 before calling u64_from_BE().

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Created by Cerberus Merlin