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Description: Attempt SSHFP lookup even if server presents a certificate |
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If an ssh server presents a certificate to the client, then the client does |
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not check the DNS for SSHFP records. This means that a malicious server can |
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essentially disable DNS-host-key-checking, which means the client will fall |
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back to asking the user (who will just say "yes" to the fingerprint, |
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sadly). |
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. |
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This is CVE-2014-2653. |
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Author: Damien Miller <djm@mindrot.org> |
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Reviewed-by: Matthew Vernon <matthew@debian.org> |
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Bug-Debian: http://bugs.debian.org/742513 |
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Forwarded: not-needed |
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Last-Update: 2014-04-03 |
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|
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Index: b/sshconnect.c |
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=================================================================== |
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--- a/sshconnect.c |
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+++ b/sshconnect.c |
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@@ -1110,29 +1110,39 @@ |
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{ |
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int flags = 0; |
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char *fp; |
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+ Key *plain = NULL; |
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|
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fp = key_fingerprint(host_key, SSH_FP_MD5, SSH_FP_HEX); |
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debug("Server host key: %s %s", key_type(host_key), fp); |
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xfree(fp); |
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|
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- /* XXX certs are not yet supported for DNS */ |
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- if (!key_is_cert(host_key) && options.verify_host_key_dns && |
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- verify_host_key_dns(host, hostaddr, host_key, &flags) == 0) { |
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- if (flags & DNS_VERIFY_FOUND) { |
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- |
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- if (options.verify_host_key_dns == 1 && |
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- flags & DNS_VERIFY_MATCH && |
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- flags & DNS_VERIFY_SECURE) |
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- return 0; |
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- |
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- if (flags & DNS_VERIFY_MATCH) { |
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- matching_host_key_dns = 1; |
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- } else { |
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- warn_changed_key(host_key); |
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- error("Update the SSHFP RR in DNS with the new " |
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- "host key to get rid of this message."); |
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+ if (options.verify_host_key_dns) { |
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+ /* |
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+ * XXX certs are not yet supported for DNS, so downgrade |
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+ * them and try the plain key. |
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+ */ |
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+ plain = key_from_private(host_key); |
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+ if (key_is_cert(plain)) |
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+ key_drop_cert(plain); |
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+ if (verify_host_key_dns(host, hostaddr, plain, &flags) == 0) { |
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+ if (flags & DNS_VERIFY_FOUND) { |
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+ if (options.verify_host_key_dns == 1 && |
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+ flags & DNS_VERIFY_MATCH && |
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+ flags & DNS_VERIFY_SECURE) { |
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+ key_free(plain); |
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+ return 0; |
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+ } |
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+ if (flags & DNS_VERIFY_MATCH) { |
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+ matching_host_key_dns = 1; |
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+ } else { |
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+ warn_changed_key(plain); |
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+ error("Update the SSHFP RR in DNS " |
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+ "with the new host key to get rid " |
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+ "of this message."); |
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+ } |
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} |
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} |
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+ key_free(plain); |
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} |
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|
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return check_host_key(host, hostaddr, options.port, host_key, RDRW, |
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