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The BN_mod_sqrt() function, which computes a modular square root, contains a bug that can cause it to loop forever for non-prime moduli. Internally this function is used when parsing certificates that contain elliptic curve public keys in compressed form or explicit elliptic curve parameters with a base point encoded in compressed form. It is possible to trigger the infinite loop by crafting a certificate that has invalid explicit curve parameters. Since certificate parsing happens prior to verification of the certificate signature, any process that parses an externally supplied certificate may thus be subject to a denial of service attack. The infinite loop can also be reached when parsing crafted private keys as they can contain explicit elliptic curve parameters. Thus vulnerable situations include: - TLS clients consuming server certificates - TLS servers consuming client certificates - Hosting providers taking certificates or private keys from customers - Certificate authorities parsing certification requests from subscribers - Anything else which parses ASN.1 elliptic curve parameters Also any other applications that use the BN_mod_sqrt() where the attacker can control the parameter values are vulnerable to this DoS issue. In the OpenSSL 1.0.2 version the public key is not parsed during initial parsing of the certificate which makes it slightly harder to trigger the infinite loop. However any operation which requires the public key from the certificate will trigger the infinite loop. In particular the attacker can use a self-signed certificate to trigger the loop during verification of the certificate signature. This issue affects OpenSSL versions 1.0.2, 1.1.1 and 3.0. It was addressed in the releases of 1.1.1n and 3.0.2 on the 15th March 2022. Fixed in OpenSSL 3.0.2 (Affected 3.0.0,3.0.1). Fixed in OpenSSL 1.1.1n (Affected 1.1.1-1.1.1m). Fixed in OpenSSL 1.0.2zd (Affected 1.0.2-1.0.2zc).
CVSS 3.1 Base Score 7.5. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
CVSS 2.0 Base Score 5. CVSS Attack Vector: network. CVSS Attack Complexity: low. CVSS Vector: (AV:N/AC:L/Au:N/C:N/I:N/A:P).
In the following code the method processMessagesFromServer attempts to establish a connection to a server and read and process messages from the server. The method uses a do/while loop to continue trying to establish the connection to the server when an attempt fails.
}
...// create socket to connect to server
}// establish connection to server// if connected then read and process messages from server
...// read and process messages// keep trying to establish connection to the server// close socket and return success or failureHowever, this will create an infinite loop if the server does not respond. This infinite loop will consume system resources and can be used to create a denial of service attack. To resolve this a counter should be used to limit the number of attempts to establish a connection to the server, as in the following code.
}
...// initialize number of attempts counter
}// establish connection to server// increment counter// if connected then read and process messages from server
...// read and process messages// keep trying to establish connection to the server// up to a maximum number of attempts// close socket and return success or failureFor this example the method isReorderNeeded as part of a bookstore application that determines if a particular book needs to be reordered based on the current inventory count and the rate at which the book is being sold.
}
return isReorder;// get inventory count for book// find number of days until inventory count reaches minimum
days++;// if number of days within reorder timeframe// set reorder return boolean to trueisReorder = true;However, the while loop will become an infinite loop if the rateSold input parameter has a value of zero since the inventoryCount will never fall below the minimumCount. In this case the input parameter should be validated to ensure that a value of zero does not cause an infinite loop,as in the following code.
}
...// validate rateSold variablereturn isReorder;ExploitPedia is constantly evolving. Sign up to receive a notification when we release additional functionality.
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