--- Begin Message ---
Package: release.debian.org
Severity: normal
Tags: bullseye
User: [email protected]
Usertags: pu
X-Debbugs-Cc: [email protected]
Control: affects -1 + src:libgit2
After fixing CVE-2023-22742 for LTS and ELTS, I'd like to see
this CVE also fixed in stable, for consistency.
The CVE is an inproper ssh certificate validation vulnerabilty,
which allows man-in-the-middle attacks.
[ Tests ]
I've manually tested the patch (checking if git poperations still
work using the ssh transport.
Autopkgtests are green too.
[ Risks ]
Manual tests and test suite works ok.
[ Checklist ]
[X] *all* changes are documented in the d/changelog
[X] I reviewed all changes and I approve them
[X] attach debdiff against the package in (old)stable
[X] the issue is verified as fixed in unstable
[ Changes ]
The change is a backport of the upstream fix:
https://github.com/libgit2/libgit2/commit/cd6f679af401eda1f172402006ef8265f8bd58ea
diff -Nru libgit2-1.1.0+dfsg.1/debian/changelog
libgit2-1.1.0+dfsg.1/debian/changelog
--- libgit2-1.1.0+dfsg.1/debian/changelog 2021-01-06 18:28:58.000000000
+0100
+++ libgit2-1.1.0+dfsg.1/debian/changelog 2023-02-24 16:11:52.000000000
+0100
@@ -1,3 +1,10 @@
+libgit2 (1.1.0+dfsg.1-4+deb11u1) bullseye-security; urgency=high
+
+ * Non-maintainer upload by the Security Team.
+ * Backport patch for CVE-2023-22742 (Closes: #1029368)
+
+ -- Tobias Frost <[email protected]> Fri, 24 Feb 2023 16:11:52 +0100
+
libgit2 (1.1.0+dfsg.1-4) unstable; urgency=medium
* Source-only upload for migration.
diff -Nru libgit2-1.1.0+dfsg.1/debian/patches/CVE-2023-22742.patch
libgit2-1.1.0+dfsg.1/debian/patches/CVE-2023-22742.patch
--- libgit2-1.1.0+dfsg.1/debian/patches/CVE-2023-22742.patch 1970-01-01
01:00:00.000000000 +0100
+++ libgit2-1.1.0+dfsg.1/debian/patches/CVE-2023-22742.patch 2023-02-24
16:11:52.000000000 +0100
@@ -0,0 +1,523 @@
+Description: CVE-2023-22742 - fails to verify SSH keys by default
+ CVE-Description: libgit2 is a cross-platform, linkable library
+ implementation of Git. When using an SSH remote with the optional libssh2
+ backend, libgit2 does not perform certificate checking by default. Prior
+ versions of libgit2 require the caller to set the `certificate_check` field of
+ libgit2's `git_remote_callbacks` structure - if a certificate check callback
is
+ not set, libgit2 does not perform any certificate checking. This means that by
+ default - without configuring a certificate check callback, clients will not
+ perform validation on the server SSH keys and may be subject to a
+ man-in-the-middle attack.
+ This is a backport of the upstream fix to the Debian stretch version.
+Origin: https://github.com/libgit2/libgit2/pull/6449
+Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1029368
+Forwarded: <URL|no|not-needed, useless if you have a Bug field, optional>
+Last-Update: 2023-02-21 <YYYY-MM-DD, last update of the meta-information,
optional>
+---
+This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
+--- a/src/transports/ssh.c
++++ b/src/transports/ssh.c
+@@ -475,15 +475,122 @@
+ return 0;
+ }
+
++
++#define KNOWN_HOSTS_FILE ".ssh/known_hosts"
++
++/*
++ * Load the known_hosts file.
++ *
++ * Returns success but leaves the output NULL if we couldn't find the file.
++ */
++static int load_known_hosts(LIBSSH2_KNOWNHOSTS **hosts, LIBSSH2_SESSION
*session)
++{
++ git_buf path = GIT_BUF_INIT;
++ LIBSSH2_KNOWNHOSTS *known_hosts = NULL;
++ int error;
++ char *home = getenv("HOME");
++
++ assert(hosts);
++
++ if (!home)
++ return GIT_ENOTFOUND;
++
++
++
++ if ((error = git_buf_join(&path, '/', home, KNOWN_HOSTS_FILE)) < 0)
++ goto out;
++
++ if ((known_hosts = libssh2_knownhost_init(session)) == NULL) {
++ ssh_error(session, "error initializing known hosts");
++ error = -1;
++ goto out;
++ }
++
++ /*
++ * Try to read the file and consider not finding it as not trusting the
++ * host rather than an error.
++ */
++ error = libssh2_knownhost_readfile(known_hosts, path.ptr,
LIBSSH2_KNOWNHOST_FILE_OPENSSH);
++ if (error == LIBSSH2_ERROR_FILE)
++ error = 0;
++ if (error < 0)
++ ssh_error(session, "error reading known_hosts");
++
++out:
++ *hosts = known_hosts;
++
++ git_buf_free(&path);
++
++ return error;
++}
++
++static const char *hostkey_type_to_string(int type)
++{
++ switch (type) {
++ case LIBSSH2_KNOWNHOST_KEY_SSHRSA:
++ return "ssh-rsa";
++ case LIBSSH2_KNOWNHOST_KEY_SSHDSS:
++ return "ssh-dss";
++#ifdef LIBSSH2_KNOWNHOST_KEY_ECDSA_256
++ case LIBSSH2_KNOWNHOST_KEY_ECDSA_256:
++ return "ecdsa-sha2-nistp256";
++ case LIBSSH2_KNOWNHOST_KEY_ECDSA_384:
++ return "ecdsa-sha2-nistp384";
++ case LIBSSH2_KNOWNHOST_KEY_ECDSA_521:
++ return "ecdsa-sha2-nistp521";
++#endif
++#ifdef LIBSSH2_KNOWNHOST_KEY_ED25519
++ case LIBSSH2_KNOWNHOST_KEY_ED25519:
++ return "ssh-ed25519";
++#endif
++ }
++
++ return NULL;
++}
++
++/*
++ * We figure out what kind of key we want to ask the remote for by trying to
++ * look it up with a nonsense key and using that mismatch to figure out what
key
++ * we do have stored for the host.
++ *
++ * Returns the string to pass to libssh2_session_method_pref or NULL if we
were
++ * unable to find anything or an error happened.
++ */
++static const char *find_hostkey_preference(LIBSSH2_KNOWNHOSTS *known_hosts,
const char *hostname, int port)
++{
++ struct libssh2_knownhost *host = NULL;
++ /* Specify no key type so we don't filter on that */
++ int type = LIBSSH2_KNOWNHOST_TYPE_PLAIN | LIBSSH2_KNOWNHOST_KEYENC_RAW;
++ const char key = '\0';
++ int error;
++
++ /*
++ * In case of mismatch, we can find the type of key from known_hosts in
++ * the returned host's information as it means that an entry was found
++ * but our nonsense key obviously didn't match.
++ */
++ error = libssh2_knownhost_checkp(known_hosts, hostname, port, &key, 1,
type, &host);
++ if (error == LIBSSH2_KNOWNHOST_CHECK_MISMATCH)
++ return hostkey_type_to_string(host->typemask &
LIBSSH2_KNOWNHOST_KEY_MASK);
++
++ return NULL;
++}
++
+ static int _git_ssh_session_create(
+ LIBSSH2_SESSION** session,
++ LIBSSH2_KNOWNHOSTS **hosts,
++ const char *hostname,
++ int port,
+ git_stream *io)
+ {
+ int rc = 0;
+ LIBSSH2_SESSION* s;
++ LIBSSH2_KNOWNHOSTS *known_hosts;
+ git_socket_stream *socket = GIT_CONTAINER_OF(io, git_socket_stream,
parent);
++ const char *keytype = NULL;
+
+ assert(session);
++ assert(hosts);
+
+ s = libssh2_session_init();
+ if (!s) {
+@@ -491,21 +598,224 @@
+ return -1;
+ }
+
++ if ((rc = load_known_hosts(&known_hosts, s)) < 0) {
++ ssh_error(s, "error loading known_hosts");
++ libssh2_session_free(s);
++ return -1;
++ }
++
++ if ((keytype = find_hostkey_preference(known_hosts, hostname, port)) !=
NULL) {
++ do {
++ rc = libssh2_session_method_pref(s,
LIBSSH2_METHOD_HOSTKEY, keytype);
++ } while (LIBSSH2_ERROR_EAGAIN == rc || LIBSSH2_ERROR_TIMEOUT ==
rc);
++ if (rc != LIBSSH2_ERROR_NONE) {
++ ssh_error(s, "failed to set hostkey preference");
++ goto on_error;
++ }
++ }
++
+ do {
+ rc = libssh2_session_handshake(s, socket->s);
+ } while (LIBSSH2_ERROR_EAGAIN == rc || LIBSSH2_ERROR_TIMEOUT == rc);
+
+ if (rc != LIBSSH2_ERROR_NONE) {
+ ssh_error(s, "failed to start SSH session");
+- libssh2_session_free(s);
+- return -1;
++ goto on_error;
+ }
+
+ libssh2_session_set_blocking(s, 1);
+
+ *session = s;
++ *hosts = known_hosts;
+
+ return 0;
++
++on_error:
++ libssh2_knownhost_free(known_hosts);
++ libssh2_session_free(s);
++ return -1;
++}
++
++
++/*
++ * Returns the typemask argument to pass to libssh2_knownhost_check{,p} based
on
++ * the type of key that libssh2_session_hostkey returns.
++ */
++static int fingerprint_type_mask(int keytype)
++{
++ int mask = LIBSSH2_KNOWNHOST_TYPE_PLAIN | LIBSSH2_KNOWNHOST_KEYENC_RAW;
++ return mask;
++
++ switch (keytype) {
++ case LIBSSH2_HOSTKEY_TYPE_RSA:
++ mask |= LIBSSH2_KNOWNHOST_KEY_SSHRSA;
++ break;
++ case LIBSSH2_HOSTKEY_TYPE_DSS:
++ mask |= LIBSSH2_KNOWNHOST_KEY_SSHDSS;
++ break;
++#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_256
++ case LIBSSH2_HOSTKEY_TYPE_ECDSA_256:
++ mask |= LIBSSH2_KNOWNHOST_KEY_ECDSA_256;
++ break;
++ case LIBSSH2_HOSTKEY_TYPE_ECDSA_384:
++ mask |= LIBSSH2_KNOWNHOST_KEY_ECDSA_384;
++ break;
++ case LIBSSH2_HOSTKEY_TYPE_ECDSA_521:
++ mask |= LIBSSH2_KNOWNHOST_KEY_ECDSA_521;
++ break;
++#endif
++#ifdef LIBSSH2_HOSTKEY_TYPE_ED25519
++ case LIBSSH2_HOSTKEY_TYPE_ED25519:
++ mask |= LIBSSH2_KNOWNHOST_KEY_ED25519;
++ break;
++#endif
++ }
++
++ return mask;
++}
++
++/*
++ * Check the host against the user's known_hosts file.
++ *
++ * Returns 1/0 for valid/''not-valid or <0 for an error
++ */
++static int check_against_known_hosts(
++ LIBSSH2_SESSION *session,
++ LIBSSH2_KNOWNHOSTS *known_hosts,
++ const char *hostname,
++ int port,
++ const char *key,
++ size_t key_len,
++ int key_type)
++{
++ int check, typemask, ret = 0;
++ struct libssh2_knownhost *host = NULL;
++
++ if (known_hosts == NULL)
++ return 0;
++
++ typemask = fingerprint_type_mask(key_type);
++ check = libssh2_knownhost_checkp(known_hosts, hostname, port, key,
key_len, typemask, &host);
++ if (check == LIBSSH2_KNOWNHOST_CHECK_FAILURE) {
++ ssh_error(session, "error checking for known host");
++ return -1;
++ }
++
++ ret = check == LIBSSH2_KNOWNHOST_CHECK_MATCH ? 1 : 0;
++
++ return ret;
++}
++
++/*
++ * Perform the check for the session's certificate against known hosts if
++ * possible and then ask the user if they have a callback.
++ *
++ * Returns 1/0 for valid/not-valid or <0 for an error
++ */
++static int check_certificate(
++ LIBSSH2_SESSION *session,
++ LIBSSH2_KNOWNHOSTS *known_hosts,
++ git_transport_certificate_check_cb check_cb,
++ void *check_cb_payload,
++ const char *host,
++ int port)
++{
++ git_cert_hostkey cert = {{ 0 }};
++ const char *key;
++ size_t cert_len;
++ int cert_type, cert_valid = 0, error = 0;
++
++ if ((key = libssh2_session_hostkey(session, &cert_len, &cert_type)) ==
NULL) {
++ ssh_error(session, "failed to retrieve hostkey");
++ return -1;
++ }
++
++ if ((cert_valid = check_against_known_hosts(session, known_hosts, host,
port, key, cert_len, cert_type)) < 0)
++ return -1;
++
++ cert.parent.cert_type = GIT_CERT_HOSTKEY_LIBSSH2;
++ if (key != NULL) {
++ cert.type |= GIT_CERT_SSH_RAW;
++ cert.hostkey = key;
++ cert.hostkey_len = cert_len;
++ switch (cert_type) {
++ case LIBSSH2_HOSTKEY_TYPE_RSA:
++ cert.raw_type = GIT_CERT_SSH_RAW_TYPE_RSA;
++ break;
++ case LIBSSH2_HOSTKEY_TYPE_DSS:
++ cert.raw_type = GIT_CERT_SSH_RAW_TYPE_DSS;
++ break;
++
++#ifdef LIBSSH2_HOSTKEY_TYPE_ECDSA_256
++ case LIBSSH2_HOSTKEY_TYPE_ECDSA_256:
++ cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_256;
++ break;
++ case LIBSSH2_HOSTKEY_TYPE_ECDSA_384:
++ cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_384;
++ break;
++ case LIBSSH2_KNOWNHOST_KEY_ECDSA_521:
++ cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_521;
++ break;
++#endif
++
++#ifdef LIBSSH2_HOSTKEY_TYPE_ED25519
++ case LIBSSH2_HOSTKEY_TYPE_ED25519:
++ cert.raw_type = GIT_CERT_SSH_RAW_TYPE_KEY_ED25519;
++ break;
++#endif
++ default:
++ cert.raw_type = GIT_CERT_SSH_RAW_TYPE_UNKNOWN;
++ }
++ }
++
++#ifdef LIBSSH2_HOSTKEY_HASH_SHA256
++ key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA256);
++ if (key != NULL) {
++ cert.type |= GIT_CERT_SSH_SHA256;
++ memcpy(&cert.hash_sha256, key, 32);
++ }
++#endif
++
++ key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA1);
++ if (key != NULL) {
++ cert.type |= GIT_CERT_SSH_SHA1;
++ memcpy(&cert.hash_sha1, key, 20);
++ }
++
++ key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_MD5);
++ if (key != NULL) {
++ cert.type |= GIT_CERT_SSH_MD5;
++ memcpy(&cert.hash_md5, key, 16);
++ }
++
++ if (cert.type == 0) {
++ git_error_set(GITERR_SSH, "unable to get the host key");
++ return -1;
++ }
++
++ git_error_clear();
++ error = 0;
++ if (!cert_valid) {
++ git_error_set(GITERR_SSH, "invalid or unknown remote ssh
hostkey");
++ error = GIT_ECERTIFICATE;
++ }
++
++ if (check_cb != NULL) {
++ git_cert_hostkey *cert_ptr = &cert;
++ git_error_state previous_error = {0};
++
++ git_error_state_capture(&previous_error, error);
++ error = check_cb((git_cert *) cert_ptr, cert_valid, host,
check_cb_payload);
++ if (error == GIT_PASSTHROUGH) {
++ error = git_error_state_restore(&previous_error);
++ } else if (error < 0 && !git_error_last()) {
++ git_error_set(GITERR_NET, "user canceled hostkey
check");
++ }
++
++ git_error_state_free(&previous_error);
++ }
++
++ return error;
+ }
+
+ #define SSH_DEFAULT_PORT "22"
+@@ -517,12 +827,13 @@
+ git_smart_subtransport_stream **stream)
+ {
+ git_net_url urldata = GIT_NET_URL_INIT;
+- int auth_methods, error = 0;
++ int auth_methods, error = 0, iport;
+ size_t i;
+ ssh_stream *s;
+ git_credential *cred = NULL;
+ LIBSSH2_SESSION* session=NULL;
+ LIBSSH2_CHANNEL* channel=NULL;
++ LIBSSH2_KNOWNHOSTS *known_hosts = NULL;
+
+ t->current_stream = NULL;
+
+@@ -557,55 +868,20 @@
+ (error = git_stream_connect(s->io)) < 0)
+ goto done;
+
+- if ((error = _git_ssh_session_create(&session, s->io)) < 0)
+- goto done;
+-
+- if (t->owner->certificate_check_cb != NULL) {
+- git_cert_hostkey cert = {{ 0 }}, *cert_ptr;
+- const char *key;
+-
+- cert.parent.cert_type = GIT_CERT_HOSTKEY_LIBSSH2;
+-
+-#ifdef LIBSSH2_HOSTKEY_HASH_SHA256
+- key = libssh2_hostkey_hash(session,
LIBSSH2_HOSTKEY_HASH_SHA256);
+- if (key != NULL) {
+- cert.type |= GIT_CERT_SSH_SHA256;
+- memcpy(&cert.hash_sha256, key, 32);
+- }
+-#endif
+-
+- key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_SHA1);
+- if (key != NULL) {
+- cert.type |= GIT_CERT_SSH_SHA1;
+- memcpy(&cert.hash_sha1, key, 20);
+- }
+-
+- key = libssh2_hostkey_hash(session, LIBSSH2_HOSTKEY_HASH_MD5);
+- if (key != NULL) {
+- cert.type |= GIT_CERT_SSH_MD5;
+- memcpy(&cert.hash_md5, key, 16);
+- }
+-
+- if (cert.type == 0) {
+- git_error_set(GIT_ERROR_SSH, "unable to get the host
key");
+- error = -1;
+- goto done;
+- }
+-
+- /* We don't currently trust any hostkeys */
+- git_error_clear();
+-
+- cert_ptr = &cert;
++ /*
++ * Try to parse the port as a number, if we can't then fall back to
++ * default. It would be nice if we could get the port that was resolved
++ * as part of the stream connection, but that's not something that's
++ * exposed.
++ */
++ iport = atol(urldata.port);
++ if(iport == 0) iport = -1;
+
+- error = t->owner->certificate_check_cb((git_cert *) cert_ptr,
0, urldata.host, t->owner->message_cb_payload);
+-
+- if (error < 0 && error != GIT_PASSTHROUGH) {
+- if (!git_error_last())
+- git_error_set(GIT_ERROR_NET, "user cancelled
hostkey check");
++ if ((error = _git_ssh_session_create(&session, &known_hosts,
urldata.host, iport, s->io)) < 0)
++ goto done;
+
+- goto done;
+- }
+- }
++ if ((error = check_certificate(session, known_hosts,
t->owner->certificate_check_cb, t->owner->message_cb_payload, urldata.host,
iport)) < 0)
++ goto done;
+
+ /* we need the username to ask for auth methods */
+ if (!urldata.username) {
+@@ -677,6 +953,9 @@
+ if (error < 0) {
+ ssh_stream_free(*stream);
+
++ if (known_hosts)
++ libssh2_knownhost_free(known_hosts);
++
+ if (session)
+ libssh2_session_free(session);
+ }
+--- a/include/git2/cert.h
++++ b/include/git2/cert.h
+@@ -80,8 +80,29 @@
+ GIT_CERT_SSH_SHA1 = (1 << 1),
+ /** SHA-256 is available */
+ GIT_CERT_SSH_SHA256 = (1 << 2),
++ /** Raw hostkey is available */
++ GIT_CERT_SSH_RAW = (1 << 3)
+ } git_cert_ssh_t;
+
++
++typedef enum {
++ /** The raw key is of an unknown type. */
++ GIT_CERT_SSH_RAW_TYPE_UNKNOWN = 0,
++ /** The raw key is an RSA key. */
++ GIT_CERT_SSH_RAW_TYPE_RSA = 1,
++ /** The raw key is a DSS key. */
++ GIT_CERT_SSH_RAW_TYPE_DSS = 2,
++ /** The raw key is a ECDSA 256 key. */
++ GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_256 = 3,
++ /** The raw key is a ECDSA 384 key. */
++ GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_384 = 4,
++ /** The raw key is a ECDSA 521 key. */
++ GIT_CERT_SSH_RAW_TYPE_KEY_ECDSA_521 = 5,
++ /** The raw key is a ED25519 key. */
++ GIT_CERT_SSH_RAW_TYPE_KEY_ED25519 = 6
++} git_cert_ssh_raw_type_t;
++
++
+ /**
+ * Hostkey information taken from libssh2
+ */
+@@ -111,6 +132,28 @@
+ * have the SHA-256 hash of the hostkey.
+ */
+ unsigned char hash_sha256[32];
++
++
++ /**
++ * Raw hostkey type. If `type` has `GIT_CERT_SSH_RAW` set, this will
++ * have the type of the raw hostkey.
++ */
++ git_cert_ssh_raw_type_t raw_type;
++
++ /**
++ * Pointer to the raw hostkey. If `type` has `GIT_CERT_SSH_RAW` set,
++ * this will have the raw contents of the hostkey.
++ */
++ const char *hostkey;
++
++ /**
++ * Raw hostkey length. If `type` has `GIT_CERT_SSH_RAW` set, this will
++ * have the length of the raw contents of the hostkey.
++ */
++ size_t hostkey_len;
++
++
++
+ } git_cert_hostkey;
+
+ /**
diff -Nru libgit2-1.1.0+dfsg.1/debian/patches/series
libgit2-1.1.0+dfsg.1/debian/patches/series
--- libgit2-1.1.0+dfsg.1/debian/patches/series 2020-12-06 23:46:54.000000000
+0100
+++ libgit2-1.1.0+dfsg.1/debian/patches/series 2023-02-24 13:05:26.000000000
+0100
@@ -1,2 +1,3 @@
disable-online-tests.patch
enable-repro-builds.patch
+CVE-2023-22742.patch
--- End Message ---
