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Merge pull request #1349 from felixc-arm/pem-integer-underflow-3.6

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[3.6] Fix Integer Underflow when Decoding PEM Keys
This commit is contained in:
David Horstmann
2025-06-04 14:36:35 +01:00
committed by GitHub
parent d9c141749b 42323eacc9
commit 3f82706cb7
3 changed files with 13 additions and 1 deletions
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5
ChangeLog.d/pem-integer-underflow.txt Normal file
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@ -0,0 +1,5 @@
Security
* Fix an integer underflow that could occur when parsing malformed PEM
keys, which could be used by an attacker capable of feeding encrypted
PEM keys to a user. This could cause a crash or information disclosure.
Found and reported by Linh Le and Ngan Nguyen from Calif.

5
library/pem.c
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@ -243,7 +243,10 @@ exit:
#if defined(MBEDTLS_DES_C) || defined(MBEDTLS_AES_C)
static int pem_check_pkcs_padding(unsigned char *input, size_t input_len, size_t *data_len)
{
/* input_len > 0 is guaranteed by mbedtls_pem_read_buffer(). */
/* input_len > 0 is not guaranteed by mbedtls_pem_read_buffer(). */
if (input_len < 1) {
return MBEDTLS_ERR_PEM_INVALID_DATA;
}
size_t pad_len = input[input_len - 1];
size_t i;

4
tests/suites/test_suite_pem.data
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@ -53,6 +53,10 @@ PEM read (malformed PEM AES-128-CBC)
depends_on:MBEDTLS_MD_CAN_MD5:MBEDTLS_AES_C:MBEDTLS_CIPHER_MODE_CBC
mbedtls_pem_read_buffer:"-----BEGIN EC PRIVATE KEY-----":"-----END EC PRIVATE KEY-----":"-----BEGIN EC PRIVATE KEY-----\nProc-Type\: 4,ENCRYPTED\nDEK-Info\: AES-128-CBC,AA94892A169FA426AA94892A169FA426\n\nMAAA\n-----END EC PRIVATE KEY-----":"pwd":MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH:""
PEM read (malformed PEM AES-128-CBC with fewer than 4 base64 chars)
depends_on:MBEDTLS_MD_CAN_MD5:MBEDTLS_AES_C:MBEDTLS_CIPHER_MODE_CBC
mbedtls_pem_read_buffer:"-----BEGIN EC PRIVATE KEY-----":"-----END EC PRIVATE KEY-----":"-----BEGIN EC PRIVATE KEY-----\nProc-Type\: 4,ENCRYPTED\nDEK-Info\: AES-128-CBC,7BA38DE00F67851E4207216809C3BB15\n\n8Q-----END EC PRIVATE KEY-----":"pwd":MBEDTLS_ERR_PEM_INVALID_DATA:""
# The output sequence's length is not multiple of block size (16 bytes). This
# proves that the pem_context->len value is properly updated based on the SEQUENCE
# length read from the decoded ASN.1 data (i.e. extra padding, if any, is ignored).