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BUG/MEDIUM: ssl/sample: check output buffer size in aes_cbc_enc converter

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AES-CBC uses a 16-byte block size, and PKCS padding always adds at least
one byte (up to a full 16 bytes when input is already block-aligned), so
the encrypted output is always larger than the input. Without checking
that the output buffer can hold the padded result, encryption could
overflow it. Add a pre-encryption guard for block cipher (blksize > 1)
that rejects the operation when the output buffer is too small.

No backport needed.

Reported-by: Omkhar Arasaratnam <omkhar@linkedin.com>
This commit is contained in:
William Lallemand 2026-05-04 17:34:13 +02:00
parent b9028ee1e4
commit 726aa2dfb2
1 changed files with 11 additions and 0 deletions
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11
src/ssl_sample.c
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@ -328,6 +328,7 @@ int aes_process(struct buffer *data, struct buffer *nonce, struct buffer *key, i
EVP_CIPHER_CTX *ctx = NULL;
int size;
int ret;
size_t blksize;
ctx = EVP_CIPHER_CTX_new();
@ -376,6 +377,16 @@ int aes_process(struct buffer *data, struct buffer *nonce, struct buffer *key, i
(unsigned char*)b_orig(nonce)))
goto err;
blksize = EVP_CIPHER_CTX_block_size(ctx);
/* https://docs.openssl.org/3.0/man3/EVP_EncryptInit/#notes
* PKCS padding works by adding n padding bytes of value n to make the
* total length of the encrypted data a multiple of the block size.
* Padding is always added so if the data is already a multiple of the
* block size n will equal the block size.
*/
if (!decrypt && blksize > 1 && (b_size(out) < (b_data(data) / blksize + 1) * blksize))
goto err;
if (aad && b_data(aad)) {
if (!sample_conv_aes_update(decrypt, ctx, NULL, (int*)&out->data,
(unsigned char*)b_orig(aad), (int)b_data(aad)))