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Description: Properly store certificate exceptions in native and java VNC viewer.
They stored the certificates as authorities, meaning that the owner of a
certificate could impersonate any server after a client had added an exception.
Author: Pierre Ossman <ossman@cendio.se> and Brian P. Hinz <bphinz@users.sf.net>
Abstract:
Properly store certificate exceptions
.
. git commit b30f10c681ec87720cff85d490f67098568a9cba
.
The previous method stored the certificates as authorities, meaning that
the owner of that certificate could impersonate any server it wanted
after a client had added an exception.
.
Handle this more properly by only storing exceptions for specific
hostname/certificate combinations, the same way browsers or SSH does
things.
.
. git commit f029745f63ac7d22fb91639b2cb5b3ab56134d6e
.
Like the native viewer, the Java viewer didn't store certificate
exceptions properly. Whilst not as bad as the native viewer, it still
failed to check that a stored certificate wouldn't be maliciously used
for another server. In practice this can in most cases be used to
impersonate another server.
.
Handle this like the native viewer by storing exceptions for a specific
hostname/certificate combination.
.
This issue is CVE-2020-26117.
Index: pkg-tigervnc/common/rfb/CSecurityTLS.cxx
===================================================================
--- pkg-tigervnc.orig/common/rfb/CSecurityTLS.cxx
+++ pkg-tigervnc/common/rfb/CSecurityTLS.cxx
@@ -250,22 +250,6 @@ void CSecurityTLS::setParam()
if (*cafile && gnutls_certificate_set_x509_trust_file(cert_cred,cafile,GNUTLS_X509_FMT_PEM) < 0)
throw AuthFailureException("load of CA cert failed");
- /* Load previously saved certs */
- char *homeDir = NULL;
- int err;
- if (getvnchomedir(&homeDir) == -1)
- vlog.error("Could not obtain VNC home directory path");
- else {
- CharArray caSave(strlen(homeDir) + 19 + 1);
- sprintf(caSave.buf, "%sx509_savedcerts.pem", homeDir);
- delete [] homeDir;
-
- err = gnutls_certificate_set_x509_trust_file(cert_cred, caSave.buf,
- GNUTLS_X509_FMT_PEM);
- if (err < 0)
- vlog.debug("Failed to load saved server certificates from %s", caSave.buf);
- }
-
if (*crlfile && gnutls_certificate_set_x509_crl_file(cert_cred,crlfile,GNUTLS_X509_FMT_PEM) < 0)
throw AuthFailureException("load of CRL failed");
@@ -290,7 +274,10 @@ void CSecurityTLS::checkSession()
const gnutls_datum_t *cert_list;
unsigned int cert_list_size = 0;
int err;
+
+ char *homeDir;
gnutls_datum_t info;
+ size_t len;
if (anon)
return;
@@ -333,13 +320,13 @@ void CSecurityTLS::checkSession()
throw AuthFailureException("decoding of certificate failed");
if (gnutls_x509_crt_check_hostname(crt, client->getServerName()) == 0) {
- char buf[255];
+ CharArray text;
vlog.debug("hostname mismatch");
- snprintf(buf, sizeof(buf), "Hostname (%s) does not match any certificate, "
- "do you want to continue?", client->getServerName());
- buf[sizeof(buf) - 1] = '\0';
- if (!msg->showMsgBox(UserMsgBox::M_YESNO, "hostname mismatch", buf))
- throw AuthFailureException("hostname mismatch");
+ text.format("Hostname (%s) does not match the server certificate, "
+ "do you want to continue?", client->getServerName());
+ if (!msg->showMsgBox(UserMsgBox::M_YESNO,
+ "Certificate hostname mismatch", text.buf))
+ throw AuthFailureException("Certificate hostname mismatch");
}
if (status == 0) {
@@ -366,87 +353,80 @@ void CSecurityTLS::checkSession()
vlog.debug("Saved server certificates don't match");
- if (gnutls_x509_crt_print(crt, GNUTLS_CRT_PRINT_ONELINE, &info)) {
- /*
- * GNUTLS doesn't correctly export gnutls_free symbol which is
- * a function pointer. Linking with Visual Studio 2008 Express will
- * fail when you call gnutls_free().
- */
-#if WIN32
- free(info.data);
-#else
- gnutls_free(info.data);
-#endif
- throw AuthFailureException("Could not find certificate to display");
+ homeDir = NULL;
+ if (getvnchomedir(&homeDir) == -1) {
+ throw AuthFailureException("Could not obtain VNC home directory "
+ "path for known hosts storage");
+ }
+
+ CharArray dbPath(strlen(homeDir) + 16 + 1);
+ sprintf(dbPath.buf, "%sx509_known_hosts", homeDir);
+ delete [] homeDir;
+
+ err = gnutls_verify_stored_pubkey(dbPath.buf, NULL,
+ client->getServerName(), NULL,
+ GNUTLS_CRT_X509, &cert_list[0], 0);
+
+ /* Previously known? */
+ if (err == GNUTLS_E_SUCCESS) {
+ vlog.debug("Server certificate found in known hosts file");
+ gnutls_x509_crt_deinit(crt);
+ return;
}
- size_t out_size = 0;
- char *out_buf = NULL;
- char *certinfo = NULL;
- int len = 0;
-
- vlog.debug("certificate issuer unknown");
-
- len = snprintf(NULL, 0, "This certificate has been signed by an unknown "
- "authority:\n\n%s\n\nDo you want to save it and "
- "continue?\n ", info.data);
- if (len < 0)
- throw AuthFailureException("certificate decoding error");
-
- vlog.debug("%s", info.data);
-
- certinfo = new char[len];
- if (certinfo == NULL)
- throw AuthFailureException("Out of memory");
-
- snprintf(certinfo, len, "This certificate has been signed by an unknown "
- "authority:\n\n%s\n\nDo you want to save it and "
- "continue? ", info.data);
-
- for (int i = 0; i < len - 1; i++)
- if (certinfo[i] == ',' && certinfo[i + 1] == ' ')
- certinfo[i] = '\n';
-
- if (!msg->showMsgBox(UserMsgBox::M_YESNO, "certificate issuer unknown",
- certinfo)) {
- delete [] certinfo;
- throw AuthFailureException("certificate issuer unknown");
- }
-
- delete [] certinfo;
-
- if (gnutls_x509_crt_export(crt, GNUTLS_X509_FMT_PEM, NULL, &out_size)
- == GNUTLS_E_SHORT_MEMORY_BUFFER)
- throw AuthFailureException("Out of memory");
-
- // Save cert
- out_buf = new char[out_size];
- if (out_buf == NULL)
- throw AuthFailureException("Out of memory");
-
- if (gnutls_x509_crt_export(crt, GNUTLS_X509_FMT_PEM, out_buf, &out_size) < 0)
- throw AuthFailureException("certificate issuer unknown, and certificate "
- "export failed");
-
- char *homeDir = NULL;
- if (getvnchomedir(&homeDir) == -1)
- vlog.error("Could not obtain VNC home directory path");
- else {
- FILE *f;
- CharArray caSave(strlen(homeDir) + 1 + 19);
- sprintf(caSave.buf, "%sx509_savedcerts.pem", homeDir);
- delete [] homeDir;
- f = fopen(caSave.buf, "a+");
- if (!f)
- msg->showMsgBox(UserMsgBox::M_OK, "certificate save failed",
- "Could not save the certificate");
- else {
- fprintf(f, "%s\n", out_buf);
- fclose(f);
- }
+ if ((err != GNUTLS_E_NO_CERTIFICATE_FOUND) &&
+ (err != GNUTLS_E_CERTIFICATE_KEY_MISMATCH)) {
+ throw AuthFailureException("Could not load known hosts database");
}
- delete [] out_buf;
+ if (gnutls_x509_crt_print(crt, GNUTLS_CRT_PRINT_ONELINE, &info))
+ throw AuthFailureException("Could not find certificate to display");
+
+ len = strlen((char*)info.data);
+ for (size_t i = 0; i < len - 1; i++) {
+ if (info.data[i] == ',' && info.data[i + 1] == ' ')
+ info.data[i] = '\n';
+ }
+
+ /* New host */
+ if (err == GNUTLS_E_NO_CERTIFICATE_FOUND) {
+ CharArray text;
+
+ vlog.debug("Server host not previously known");
+ vlog.debug("%s", info.data);
+
+ text.format("This certificate has been signed by an unknown "
+ "authority:\n\n%s\n\nSomeone could be trying to "
+ "impersonate the site and you should not "
+ "continue.\n\nDo you want to make an exception "
+ "for this server?", info.data);
+
+ if (!msg->showMsgBox(UserMsgBox::M_YESNO,
+ "Unknown certificate issuer",
+ text.buf))
+ throw AuthFailureException("Unknown certificate issuer");
+ } else if (err == GNUTLS_E_CERTIFICATE_KEY_MISMATCH) {
+ CharArray text;
+
+ vlog.debug("Server host key mismatch");
+ vlog.debug("%s", info.data);
+
+ text.format("This host is previously known with a different "
+ "certificate, and the new certificate has been "
+ "signed by an unknown authority:\n\n%s\n\nSomeone "
+ "could be trying to impersonate the site and you "
+ "should not continue.\n\nDo you want to make an "
+ "exception for this server?", info.data);
+
+ if (!msg->showMsgBox(UserMsgBox::M_YESNO,
+ "Unexpected server certificate",
+ text.buf))
+ throw AuthFailureException("Unexpected server certificate");
+ }
+
+ if (gnutls_store_pubkey(dbPath.buf, NULL, client->getServerName(),
+ NULL, GNUTLS_CRT_X509, &cert_list[0], 0, 0))
+ vlog.error("Failed to store server certificate to known hosts database");
gnutls_x509_crt_deinit(crt);
/*
Index: pkg-tigervnc/java/com/tigervnc/rfb/CSecurityTLS.java
===================================================================
--- pkg-tigervnc.orig/java/com/tigervnc/rfb/CSecurityTLS.java
+++ pkg-tigervnc/java/com/tigervnc/rfb/CSecurityTLS.java
@@ -107,12 +107,6 @@ public class CSecurityTLS extends CSecur
X509CRL.setDefaultStr(getDefaultCRL());
}
-// FIXME:
-// Need to shutdown the connection cleanly
-
-// FIXME?
-// add a finalizer method that calls shutdown
-
public boolean processMsg(CConnection cc) {
is = (FdInStream)cc.getInStream();
os = (FdOutStream)cc.getOutStream();
@@ -269,8 +263,13 @@ public class CSecurityTLS extends CSecur
{
Collection<? extends Certificate> certs = null;
X509Certificate cert = chain[0];
+ String pk =
+ Base64.getEncoder().encodeToString(cert.getPublicKey().getEncoded());
try {
cert.checkValidity();
+ verifyHostname(cert);
+ } catch(CertificateParsingException e) {
+ throw new SystemException(e.getMessage());
} catch(CertificateNotYetValidException e) {
throw new AuthFailureException("server certificate has not been activated");
} catch(CertificateExpiredException e) {
@@ -279,73 +278,111 @@ public class CSecurityTLS extends CSecur
"do you want to continue?"))
throw new AuthFailureException("server certificate has expired");
}
- String thumbprint = getThumbprint(cert);
File vncDir = new File(FileUtils.getVncHomeDir());
- File certFile = new File(vncDir, "x509_savedcerts.pem");
- CertificateFactory cf = CertificateFactory.getInstance("X.509");
- if (vncDir.exists() && certFile.exists() && certFile.canRead()) {
- InputStream certStream = new MyFileInputStream(certFile);
- certs = cf.generateCertificates(certStream);
- for (Certificate c : certs)
- if (thumbprint.equals(getThumbprint((X509Certificate)c)))
- return;
- }
+ if (!vncDir.exists())
+ throw new AuthFailureException("Could not obtain VNC home directory "+
+ "path for known hosts storage");
+ File dbPath = new File(vncDir, "x509_known_hosts");
+ String info =
+ " Subject: "+cert.getSubjectX500Principal().getName()+"\n"+
+ " Issuer: "+cert.getIssuerX500Principal().getName()+"\n"+
+ " Serial Number: "+cert.getSerialNumber()+"\n"+
+ " Version: "+cert.getVersion()+"\n"+
+ " Signature Algorithm: "+cert.getPublicKey().getAlgorithm()+"\n"+
+ " Not Valid Before: "+cert.getNotBefore()+"\n"+
+ " Not Valid After: "+cert.getNotAfter()+"\n"+
+ " SHA-1 Fingerprint: "+getThumbprint(cert)+"\n";
try {
- verifyHostname(cert);
+ if (dbPath.exists()) {
+ FileReader db = new FileReader(dbPath);
+ BufferedReader dbBuf = new BufferedReader(db);
+ String line;
+ String server = client.getServerName().toLowerCase();
+ while ((line = dbBuf.readLine())!=null) {
+ String fields[] = line.split("\\|");
+ if (fields.length==6) {
+ if (server.equals(fields[2]) && pk.equals(fields[5])) {
+ vlog.debug("Server certificate found in known hosts file");
+ dbBuf.close();
+ return;
+ } else if (server.equals(fields[2]) && !pk.equals(fields[5]) ||
+ !server.equals(fields[2]) && pk.equals(fields[5])) {
+ throw new CertStoreException();
+ }
+ }
+ }
+ dbBuf.close();
+ }
tm.checkServerTrusted(chain, authType);
+ } catch (IOException e) {
+ throw new AuthFailureException("Could not load known hosts database");
+ } catch (CertStoreException e) {
+ vlog.debug("Server host key mismatch");
+ vlog.debug(info);
+ String text =
+ "This host is previously known with a different "+
+ "certificate, and the new certificate has been "+
+ "signed by an unknown authority\n"+
+ "\n"+info+"\n"+
+ "Someone could be trying to impersonate the site and you should not continue.\n"+
+ "\n"+
+ "Do you want to make an exception for this server?";
+ if (!msg.showMsgBox(YES_NO_OPTION, "Unexpected certificate issuer", text))
+ throw new AuthFailureException("Unexpected certificate issuer");
+ store_pubkey(dbPath, client.getServerName().toLowerCase(), pk);
} catch (java.lang.Exception e) {
if (e.getCause() instanceof CertPathBuilderException) {
- String certinfo =
+ vlog.debug("Server host not previously known");
+ vlog.debug(info);
+ String text =
"This certificate has been signed by an unknown authority\n"+
+ "\n"+info+"\n"+
+ "Someone could be trying to impersonate the site and you should not continue.\n"+
"\n"+
- " Subject: "+cert.getSubjectX500Principal().getName()+"\n"+
- " Issuer: "+cert.getIssuerX500Principal().getName()+"\n"+
- " Serial Number: "+cert.getSerialNumber()+"\n"+
- " Version: "+cert.getVersion()+"\n"+
- " Signature Algorithm: "+cert.getPublicKey().getAlgorithm()+"\n"+
- " Not Valid Before: "+cert.getNotBefore()+"\n"+
- " Not Valid After: "+cert.getNotAfter()+"\n"+
- " SHA1 Fingerprint: "+getThumbprint(cert)+"\n"+
- "\n"+
- "Do you want to save it and continue?";
- if (!msg.showMsgBox(YES_NO_OPTION, "certificate issuer unknown",
- certinfo)) {
- throw new AuthFailureException("certificate issuer unknown");
- }
- if (certs == null || !certs.contains(cert)) {
- byte[] der = cert.getEncoded();
- String pem = Base64.getEncoder().encodeToString(der);
- pem = pem.replaceAll("(.{64})", "$1\n");
- FileWriter fw = null;
- try {
- if (!vncDir.exists())
- vncDir.mkdir();
- if (!certFile.exists() && !certFile.createNewFile()) {
- vlog.error("Certificate save failed.");
- } else {
- fw = new FileWriter(certFile.getAbsolutePath(), true);
- fw.write("-----BEGIN CERTIFICATE-----\n");
- fw.write(pem+"\n");
- fw.write("-----END CERTIFICATE-----\n");
- }
- } catch (IOException ioe) {
- msg.showMsgBox(OK_OPTION, "certificate save failed",
- "Could not save the certificate");
- } finally {
- try {
- if (fw != null)
- fw.close();
- } catch(IOException ioe2) {
- throw new Exception(ioe2.getMessage());
- }
- }
- }
+ "Do you want to make an exception for this server?";
+ if (!msg.showMsgBox(YES_NO_OPTION, "Unknown certificate issuer", text))
+ throw new AuthFailureException("Unknown certificate issuer");
+ store_pubkey(dbPath, client.getServerName().toLowerCase(), pk);
} else {
throw new SystemException(e.getMessage());
}
}
}
+ private void store_pubkey(File dbPath, String serverName, String pk)
+ {
+ ArrayList<String> lines = new ArrayList<String>();
+ File vncDir = new File(FileUtils.getVncHomeDir());
+ try {
+ if (dbPath.exists()) {
+ FileReader db = new FileReader(dbPath);
+ BufferedReader dbBuf = new BufferedReader(db);
+ String line;
+ while ((line = dbBuf.readLine())!=null) {
+ String fields[] = line.split("\\|");
+ if (fields.length==6)
+ if (!serverName.equals(fields[2]) && !pk.equals(fields[5]))
+ lines.add(line);
+ }
+ dbBuf.close();
+ }
+ } catch (IOException e) {
+ throw new AuthFailureException("Could not load known hosts database");
+ }
+ try {
+ if (!dbPath.exists())
+ dbPath.createNewFile();
+ FileWriter fw = new FileWriter(dbPath.getAbsolutePath(), false);
+ Iterator i = lines.iterator();
+ while (i.hasNext())
+ fw.write((String)i.next()+"\n");
+ fw.write("|g0|"+serverName+"|*|0|"+pk+"\n");
+ fw.close();
+ } catch (IOException e) {
+ vlog.error("Failed to store server certificate to known hosts database");
+ }
+ }
+
public X509Certificate[] getAcceptedIssuers ()
{
return tm.getAcceptedIssuers();
@@ -399,12 +436,13 @@ public class CSecurityTLS extends CSecur
}
Object[] answer = {"YES", "NO"};
int ret = JOptionPane.showOptionDialog(null,
- "Hostname verification failed. Do you want to continue?",
- "Hostname Verification Failure",
+ "Hostname ("+client.getServerName()+") does not match the"+
+ " server certificate, do you want to continue?",
+ "Certificate hostname mismatch",
JOptionPane.YES_NO_OPTION, JOptionPane.WARNING_MESSAGE,
null, answer, answer[0]);
if (ret != JOptionPane.YES_OPTION)
- throw new WarningException("Hostname verification failed.");
+ throw new WarningException("Certificate hostname mismatch.");
} catch (CertificateParsingException e) {
throw new SystemException(e.getMessage());
} catch (InvalidNameException e) {
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