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Check the received uncompressed certificate length to prevent excessive
pre-decompression allocation. The patch was proposed by Tomas Dulka and Stanislav Fort (Aisle Research). Fixes: CVE-2025-66199 Reviewed-by: Saša Nedvědický <sashan@openssl.org> Reviewed-by: Tomas Mraz <tomas@openssl.org> MergeDate: Mon Jan 26 19:45:21 2026 (cherry picked from commit 84f73f7)
1 parent 68a7cd2 commit 966a247

3 files changed

Lines changed: 48 additions & 1 deletion

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‎ssl/statem/statem_lib.c‎

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2899,6 +2899,12 @@ MSG_PROCESS_RETURN tls13_process_compressed_certificate(SSL_CONNECTION *sc,
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goto err;
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}
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/* Prevent excessive pre-decompression allocation */
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if (expected_length > sc->max_cert_list) {
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SSLfatal(sc, SSL_AD_BAD_CERTIFICATE, SSL_R_EXCESSIVE_MESSAGE_SIZE);
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goto err;
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}
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if (PACKET_remaining(pkt) != comp_length || comp_length == 0) {
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SSLfatal(sc, SSL_AD_DECODE_ERROR, SSL_R_BAD_DECOMPRESSION);
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goto err;

‎test/recipes/70-test_tls13certcomp.t‎

Lines changed: 41 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,7 @@ use OpenSSL::Test qw/:DEFAULT cmdstr srctop_file srctop_dir bldtop_dir/;
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use OpenSSL::Test::Utils;
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use File::Temp qw(tempfile);
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use TLSProxy::Proxy;
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use TLSProxy::Message;
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use checkhandshake qw(checkhandshake @handmessages @extensions);
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my $test_name = "test_tls13certcomp";
@@ -220,7 +221,7 @@ $proxy->clear();
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$proxy->serverflags("-no_tx_cert_comp -no_rx_cert_comp");
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# One final skip check
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$proxy->start() or plan skip_all => "Unable to start up Proxy for tests";
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plan tests => 8;
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plan tests => 9;
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checkhandshake($proxy, checkhandshake::DEFAULT_HANDSHAKE,
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checkhandshake::DEFAULT_EXTENSIONS
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| checkhandshake::CERT_COMP_CLI_EXTENSION,
@@ -296,3 +297,42 @@ $proxy->start();
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checkhandshake($proxy, checkhandshake::DEFAULT_HANDSHAKE,
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checkhandshake::DEFAULT_EXTENSIONS,
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"Send but not accept compressed certificates");
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#Test 9: Excessive uncompressed certificate length in CompressedCertificate
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$proxy->clear();
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$proxy->filter(\&excessive_uncompressed_len_filter);
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$proxy->serverflags("-cert_comp");
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$proxy->start();
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ok(is_alert_message(TLSProxy::Message::AL_DESC_BAD_CERTIFICATE),
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"Excessive uncompressed certificate length rejected");
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my $done = 0;
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sub excessive_uncompressed_len_filter
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{
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my $proxy = shift;
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return if $done;
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foreach my $m (@{$proxy->message_list}) {
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next unless $m->mt == TLSProxy::Message::MT_COMPRESSED_CERTIFICATE;
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my $data = $m->data;
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# RFC8879 CompressedCertificate:
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# uint16 algorithm; uint24 uncompressed_length; ...
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substr($data, 2, 3) = "\xFF\xFF\xFF"; # uncompressed_length
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$m->data($data);
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$m->repack();
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$done = 1;
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last;
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}
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}
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# Test if the last message was a failure and matches the expected type.
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sub is_alert_message
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{
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my $alert_type = shift;
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return 0 unless TLSProxy::Message->fail();
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return 1 if TLSProxy::Message->alert->description() == $alert_type;
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return 0;
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}

‎util/perl/TLSProxy/Message.pm‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -45,6 +45,7 @@ use constant {
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AL_DESC_CLOSE_NOTIFY => 0,
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AL_DESC_UNEXPECTED_MESSAGE => 10,
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AL_DESC_BAD_RECORD_MAC => 20,
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AL_DESC_BAD_CERTIFICATE => 42,
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AL_DESC_ILLEGAL_PARAMETER => 47,
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AL_DESC_DECODE_ERROR => 50,
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AL_DESC_PROTOCOL_VERSION => 70,

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