From 1f2731f5d7a8f8a8385c6031667ed29072c0d92a Mon Sep 17 00:00:00 2001 From: "djm@openbsd.org" Date: Wed, 19 Jul 2023 13:56:33 +0000 Subject: [PATCH 4/4] upstream: Disallow remote addition of FIDO/PKCS11 provider libraries to ssh-agent by default. The old behaviour of allowing remote clients from loading providers can be restored using `ssh-agent -O allow-remote-pkcs11`. Detection of local/remote clients requires a ssh(1) that supports the `session-bind@openssh.com` extension. Forwarding access to a ssh-agent socket using non-OpenSSH tools may circumvent this control. ok markus@ OpenBSD-Commit-ID: 4c2bdf79b214ae7e60cc8c39a45501344fa7bd7c Upstream-Status: Backport [https://github.com/openssh/openssh-portable/commit/1f2731f5d7a8f8a8385c6031667ed29072c0d92a] CVE: CVE-2023-38408 Signed-off-by: Archana Polampalli --- ssh-agent.1 | 21 +++++++++++++++++++++ ssh-agent.c | 21 ++++++++++++++++++++- 2 files changed, 41 insertions(+), 1 deletion(-) diff --git a/ssh-agent.1 b/ssh-agent.1 index ed8c870..15d0a47 100644 --- a/ssh-agent.1 +++ b/ssh-agent.1 @@ -102,6 +102,27 @@ The default is Kill the current agent (given by the .Ev SSH_AGENT_PID environment variable). +Currently two options are supported: +.Cm allow-remote-pkcs11 +and +.Cm no-restrict-websafe . +.Pp +The +.Cm allow-remote-pkcs11 +option allows clients of a forwarded +.Nm +to load PKCS#11 or FIDO provider libraries. +By default only local clients may perform this operation. +Note that signalling that a +.Nm +client remote is performed by +.Xr ssh 1 , +and use of other tools to forward access to the agent socket may circumvent +this restriction. +.Pp +The +.Cm no-restrict-websafe , +instructs .It Fl P Ar allowed_providers Specify a pattern-list of acceptable paths for PKCS#11 provider and FIDO authenticator middleware shared libraries that may be used with the diff --git a/ssh-agent.c b/ssh-agent.c index 03ae2b0..19eeaae 100644 --- a/ssh-agent.c +++ b/ssh-agent.c @@ -171,6 +171,12 @@ char socket_dir[PATH_MAX]; /* Pattern-list of allowed PKCS#11/Security key paths */ static char *allowed_providers; +/* + * Allows PKCS11 providers or SK keys that use non-internal providers to + * be added over a remote connection (identified by session-bind@openssh.com). + */ +static int remote_add_provider; + /* locking */ #define LOCK_SIZE 32 #define LOCK_SALT_SIZE 16 @@ -1239,6 +1245,12 @@ process_add_identity(SocketEntry *e) if (strcasecmp(sk_provider, "internal") == 0) { debug_f("internal provider"); } else { + if (e->nsession_ids != 0 && !remote_add_provider) { + verbose("failed add of SK provider \"%.100s\": " + "remote addition of providers is disabled", + sk_provider); + goto out; + } if (realpath(sk_provider, canonical_provider) == NULL) { verbose("failed provider \"%.100s\": " "realpath: %s", sk_provider, @@ -1402,6 +1414,11 @@ process_add_smartcard_key(SocketEntry *e) error_f("failed to parse constraints"); goto send; } + if (e->nsession_ids != 0 && !remote_add_provider) { + verbose("failed PKCS#11 add of \"%.100s\": remote addition of " + "providers is disabled", provider); + goto send; + } if (realpath(provider, canonical_provider) == NULL) { verbose("failed PKCS#11 add of \"%.100s\": realpath: %s", provider, strerror(errno)); @@ -2061,7 +2078,9 @@ main(int ac, char **av) break; case 'O': if (strcmp(optarg, "no-restrict-websafe") == 0) - restrict_websafe = 0; + restrict_websafe = 0; + else if (strcmp(optarg, "allow-remote-pkcs11") == 0) + remote_add_provider = 1; else fatal("Unknown -O option"); break; -- 2.40.0