From 8780a896543a654e757db1b9396383f9d8095528 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Thu, 6 Jul 2023 16:36:35 +0100 Subject: [PATCH] Fix DH_check() excessive time with over sized modulus The DH_check() function checks numerous aspects of the key or parameters that have been supplied. Some of those checks use the supplied modulus value even if it is excessively large. There is already a maximum DH modulus size (10,000 bits) over which OpenSSL will not generate or derive keys. DH_check() will however still perform various tests for validity on such a large modulus. We introduce a new maximum (32,768) over which DH_check() will just fail. An application that calls DH_check() and supplies a key or parameters obtained from an untrusted source could be vulnerable to a Denial of Service attack. The function DH_check() is itself called by a number of other OpenSSL functions. An application calling any of those other functions may similarly be affected. The other functions affected by this are DH_check_ex() and EVP_PKEY_param_check(). CVE-2023-3446 Reviewed-by: Paul Dale Reviewed-by: Tom Cosgrove Reviewed-by: Bernd Edlinger Reviewed-by: Tomas Mraz (Merged from https://github.com/openssl/openssl/pull/21452) diff -wpruN --no-dereference '--exclude=*.orig' a~/crypto/dh/dh.h a/crypto/dh/dh.h --- a~/crypto/dh/dh.h 1970-01-01 00:00:00 +++ a/crypto/dh/dh.h 1970-01-01 00:00:00 @@ -76,6 +76,9 @@ # ifndef OPENSSL_DH_MAX_MODULUS_BITS # define OPENSSL_DH_MAX_MODULUS_BITS 10000 # endif +# ifndef OPENSSL_DH_CHECK_MAX_MODULUS_BITS +# define OPENSSL_DH_CHECK_MAX_MODULUS_BITS 32768 +# endif # define DH_FLAG_CACHE_MONT_P 0x01 @@ -363,6 +366,7 @@ int DH_KDF_X9_42(unsigned char *out, siz * The following lines are auto generated by the script mkerr.pl. Any changes * made after this point may be overwritten when the script is next run. */ + void ERR_load_DH_strings(void); /* Error codes for the DH functions. */ @@ -371,6 +375,7 @@ void ERR_load_DH_strings(void); # define DH_F_COMPUTE_KEY 102 # define DH_F_DHPARAMS_PRINT_FP 101 # define DH_F_DH_BUILTIN_GENPARAMS 106 +# define DH_F_DH_CHECK 120 # define DH_F_DH_CMS_DECRYPT 117 # define DH_F_DH_CMS_SET_PEERKEY 118 # define DH_F_DH_CMS_SET_SHARED_INFO 119 diff -wpruN --no-dereference '--exclude=*.orig' a~/crypto/dh/dh_check.c a/crypto/dh/dh_check.c --- a~/crypto/dh/dh_check.c 1970-01-01 00:00:00 +++ a/crypto/dh/dh_check.c 1970-01-01 00:00:00 @@ -78,6 +78,12 @@ int DH_check(const DH *dh, int *ret) BN_ULONG l; BIGNUM *t1 = NULL, *t2 = NULL; + /* Don't do any checks at all with an excessively large modulus */ + if (BN_num_bits(dh->p) > OPENSSL_DH_CHECK_MAX_MODULUS_BITS) { + DHerr(DH_F_DH_CHECK, DH_R_MODULUS_TOO_LARGE); + return 0; + } + *ret = 0; ctx = BN_CTX_new(); if (ctx == NULL) diff -wpruN --no-dereference '--exclude=*.orig' a~/crypto/dh/dh_err.c a/crypto/dh/dh_err.c --- a~/crypto/dh/dh_err.c 1970-01-01 00:00:00 +++ a/crypto/dh/dh_err.c 1970-01-01 00:00:00 @@ -1,6 +1,6 @@ /* crypto/dh/dh_err.c */ /* ==================================================================== - * Copyright (c) 1999-2013 The OpenSSL Project. All rights reserved. + * Copyright (c) 1999-2023 The OpenSSL Project. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions @@ -73,6 +73,7 @@ static ERR_STRING_DATA DH_str_functs[] = {ERR_FUNC(DH_F_COMPUTE_KEY), "COMPUTE_KEY"}, {ERR_FUNC(DH_F_DHPARAMS_PRINT_FP), "DHparams_print_fp"}, {ERR_FUNC(DH_F_DH_BUILTIN_GENPARAMS), "DH_BUILTIN_GENPARAMS"}, + {ERR_FUNC(DH_F_DH_CHECK), "DH_check"}, {ERR_FUNC(DH_F_DH_CMS_DECRYPT), "DH_CMS_DECRYPT"}, {ERR_FUNC(DH_F_DH_CMS_SET_PEERKEY), "DH_CMS_SET_PEERKEY"}, {ERR_FUNC(DH_F_DH_CMS_SET_SHARED_INFO), "DH_CMS_SET_SHARED_INFO"},