*** This bug is a security vulnerability ***
Public security bug reported:
In FIPS mode on Bionic MD5 is semi-disabled causing some applications to
segfault.
Test case:
sudo apt install ntp
ntpq -p
Segmentation fault (core dumped)
What happens there is ntpq wants to iterate all available digests
(list_digest_names in ntpq.c). It uses EVP_MD_do_all_sorted for this
task.
EVP_MD_do_all_sorted eventually runs openssl_add_all_digests_int in c_alld.c.
For FIPS mode it adds:
EVP_add_digest(EVP_md5());
What happens later in ntpq is (list_md_fn function inside ntpq.c):
ctx = EVP_MD_CTX_new();
EVP_DigestInit(ctx, EVP_get_digestbyname(name));
EVP_DigestFinal(ctx, digest, &digest_len);
First digest it gets is MD5, but while running EVP_DigestInit for it, it gets
to this point:
#ifdef OPENSSL_FIPS
if (FIPS_mode()) {
if (!(type->flags & EVP_MD_FLAG_FIPS)
&& !(ctx->flags & EVP_MD_CTX_FLAG_NON_FIPS_ALLOW)) {
EVPerr(EVP_F_EVP_DIGESTINIT_EX, EVP_R_DISABLED_FOR_FIPS);
return 0;
}
}
#endif
Due to type->flags for MD5 being 0 there's an error set
(EVP_R_DISABLED_FOR_FIPS).
After getting back to ntpq.c:
ctx->engine and ctx->digest are not set (due to the mentioned error), hence
inside EVP_DigestFinal_ex (openssl/crypto/evp/digest.c)
OPENSSL_assert(ctx->digest->md_size <= EVP_MAX_MD_SIZE);
causes a segfault (ctx->digest is NULL).
So either MD5 shouldn't be added in FIPS mode or it should have the
EVP_MD_FLAG_FIPS to be properly initialized.
** Affects: openssl (Ubuntu)
Importance: Medium
Status: New
** Affects: openssl (Ubuntu Bionic)
Importance: Medium
Status: New
** Tags: sts
** Also affects: openssl (Ubuntu Bionic)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1884265
Title:
[fips] Not fully initialized digest segfaulting some client
applications
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