CVE-2023-2650

Issue summary: Processing some specially crafted ASN.1 object identifiers or

data containing them may be very slow.

Impact summary: Applications that use OBJ_obj2txt() directly, or use any of

the OpenSSL subsystems OCSP, PKCS7/SMIME, CMS, CMP/CRMF or TS with no message

size limit may experience notable to very long delays when processing those

messages, which may lead to a Denial of Service.

An OBJECT IDENTIFIER is composed of a series of numbers - sub-identifiers -

most of which have no size limit. OBJ_obj2txt() may be used to translate

an ASN.1 OBJECT IDENTIFIER given in DER encoding form (using the OpenSSL

type ASN1_OBJECT) to its canonical numeric text form, which are the

sub-identifiers of the OBJECT IDENTIFIER in decimal form, separated by

periods.

When one of the sub-identifiers in the OBJECT IDENTIFIER is very large

(these are sizes that are seen as absurdly large, taking up tens or hundreds

of KiBs), the translation to a decimal number in text may take a very long

time. The time complexity is O(n^2) with 'n' being the size of the

sub-identifiers in bytes (*).

With OpenSSL 3.0, support to fetch cryptographic algorithms using names /

identifiers in string form was introduced. This includes using OBJECT

IDENTIFIERs in canonical numeric text form as identifiers for fetching

algorithms.

Such OBJECT IDENTIFIERs may be received through the ASN.1 structure

AlgorithmIdentifier, which is commonly used in multiple protocols to specify

what cryptographic algorithm should be used to sign or verify, encrypt or

decrypt, or digest passed data.

Applications that call OBJ_obj2txt() directly with untrusted data are

affected, with any version of OpenSSL. If the use is for the mere purpose

of display, the severity is considered low.

In OpenSSL 3.0 and newer, this affects the subsystems OCSP, PKCS7/SMIME,

CMS, CMP/CRMF or TS. It also impacts anything that processes X.509

certificates, including simple things like verifying its signature.

The impact on TLS is relatively low, because all versions of OpenSSL have a

100KiB limit on the peer's certificate chain. Additionally, this only

impacts clients, or servers that have explicitly enabled client

authentication.

In OpenSSL 1.1.1 and 1.0.2, this only affects displaying diverse objects,

such as X.509 certificates. This is assumed to not happen in such a way

that it would cause a Denial of Service, so these versions are considered

not affected by this issue in such a way that it would be cause for concern,

and the severity is therefore considered low.