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pem: Avoid integer underflow when verifying padding after decryption

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If the padding was larger than the whole blob, all available bytes were
checked for a match and the blob's length was eventually adjusted and
SUCCESS returned.  Due to the underflow this could result in a huge size
that would then get copied.  Zero-length padding was also incorrectly
accepted as was padding larger than the block size.

Fixes: 160f4c225d ("moved PEM parsing functionality to its own plugin")
This commit is contained in:
Tobias Brunner
2026-07-24 08:47:39 +02:00
parent 94e97eb183
commit 52b689c4f8
1 changed files with 7 additions and 8 deletions
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src/libstrongswan/plugins/pem/pem_builder.c
+7 -8
View File
@@ -95,6 +95,7 @@ static status_t pem_decrypt(chunk_t *blob, encryption_algorithm_t alg,
chunk_t decrypted; chunk_t decrypted;
chunk_t key = {alloca(key_size), key_size}; chunk_t key = {alloca(key_size), key_size};
uint8_t padding, *last_padding_pos, *first_padding_pos; uint8_t padding, *last_padding_pos, *first_padding_pos;
size_t block_size;
if (!key_size) if (!key_size)
{ {
@@ -141,8 +142,8 @@ static status_t pem_decrypt(chunk_t *blob, encryption_algorithm_t alg,
return NOT_SUPPORTED; return NOT_SUPPORTED;
} }
if (iv.len != crypter->get_iv_size(crypter) || block_size = crypter->get_block_size(crypter);
blob->len % crypter->get_block_size(crypter)) if (iv.len != crypter->get_iv_size(crypter) || blob->len % block_size)
{ {
DBG1(DBG_ASN, " data size is not multiple of block size"); DBG1(DBG_ASN, " data size is not multiple of block size");
crypter->destroy(crypter); crypter->destroy(crypter);
@@ -164,14 +165,12 @@ static status_t pem_decrypt(chunk_t *blob, encryption_algorithm_t alg,
/* determine amount of padding */ /* determine amount of padding */
last_padding_pos = blob->ptr + blob->len - 1; last_padding_pos = blob->ptr + blob->len - 1;
padding = *last_padding_pos; padding = *last_padding_pos;
if (padding > blob->len) if (!padding || padding > block_size)
{ {
first_padding_pos = blob->ptr; DBG1(DBG_ASN, " invalid passphrase");
} return INVALID_ARG;
else
{
first_padding_pos = last_padding_pos - padding;
} }
first_padding_pos = last_padding_pos - padding;
/* check the padding pattern */ /* check the padding pattern */
while (--last_padding_pos > first_padding_pos) while (--last_padding_pos > first_padding_pos)
{ {