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Fix out-of-bounds read in ASN.1 type-and-length parser #589

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Merged
kazuho merged 1 commit into from
Apr 9, 2026
Merged

Fix out-of-bounds read in ASN.1 type-and-length parser #589

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5 changes: 5 additions & 0 deletions lib/asn1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -183,6 +183,11 @@ size_t ptls_asn1_get_expected_type_and_length(const uint8_t *bytes, size_t bytes
{
int is_indefinite = 0;

if (byte_index >= bytes_max) {
*decode_error = PTLS_ERROR_INCORRECT_ASN1_SYNTAX;
return ptls_asn1_error_message("Unexpected end of input", bytes_max, byte_index, 0, log_ctx);
}

/* Check that the expected type is present */
if (bytes[byte_index] != expected_type) {
byte_index = ptls_asn1_error_message("Unexpected type", bytes_max, byte_index, 0, log_ctx);
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22 changes: 22 additions & 0 deletions t/minicrypto.c
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Expand Up @@ -28,6 +28,7 @@
#include "../deps/picotest/picotest.h"
#include "../lib/cifra.c"
#include "../lib/uecc.c"
#include "picotls/asn1.h"
#include "test.h"

static void test_secp256r1_key_exchange(void)
Expand Down Expand Up @@ -135,6 +136,26 @@ static void test_hrr(void)
ptls_free(server);
}

static void test_asn1_empty_input(void)
{
int decode_error = 0;
uint32_t length = 0;
size_t last_byte = 0;
uint8_t dummy = 0x30;

ptls_asn1_get_expected_type_and_length(&dummy, 0, 0, 0x30, &length, NULL, &last_byte, &decode_error, NULL);
ok(decode_error != 0);

decode_error = 0;
uint8_t buf[2] = {0x30, 0x00};
ptls_asn1_get_expected_type_and_length(buf, 2, 2, 0x30, &length, NULL, &last_byte, &decode_error, NULL);
ok(decode_error != 0);

decode_error = 0;
ptls_asn1_get_expected_type_and_length(buf, 1, 1, 0x04, &length, NULL, &last_byte, &decode_error, NULL);
ok(decode_error != 0);
}

DEFINE_FFX_AES128_ALGORITHMS(minicrypto);
DEFINE_FFX_CHACHA20_ALGORITHMS(minicrypto);

Expand All @@ -161,6 +182,7 @@ int main(int argc, char **argv)
ADD_FFX_CHACHA20_ALGORITHMS(minicrypto);

subtest("picotls", test_picotls);
subtest("asn1-bounds", test_asn1_empty_input);
subtest("hrr", test_hrr);

return done_testing();
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