Patch Package:           OTP 27.3.4.18
Git Tag:                 OTP-27.3.4.18
Date:                    2026-09-22
Trouble Report Id:       OTP-20256, OTP-20272, OTP-20287, OTP-20327,
                         OTP-20355, OTP-20358, OTP-20365, OTP-20367,
                         OTP-20371, OTP-20384, OTP-20386, OTP-20388,
                         OTP-20390
Seq num:                 CVE-2026-65634, CVE-2026-68956,
                         CVE-2026-89422, ERIERL-1355, ERIERL-1356,
                         ERIERL-1363, GH-11338, GH-11344, GH-11534,
                         GH-11586, GH-11619, GH-SA-qhcm-px9c-rvfh,
                         PR-11356, PR-11426, PR-11523, PR-11559,
                         PR-11566, PR-11570, PR-11574, PR-11616,
                         PR-11632, PR-11638, PR-11641, PR-11651,
                         PR-11655
System:                  OTP
Release:                 27
Application:             asn1-5.3.4.3, compiler-8.6.1.7,
                         mnesia-4.23.5.5, public_key-1.17.1.6,
                         ssh-5.2.11.13, ssl-11.2.12.13
Predecessor:             OTP 27.3.4.17

Check out the git tag OTP-27.3.4.18, and build a full OTP system including
documentation. Apply one or more applications from this build as patches to your
installation using the ‘otp_patch_apply’ tool. For information on install
requirements, see descriptions for each application version below.

POTENTIAL INCOMPATIBILITIES

• Fixed a vulnerability where the max_channels daemon option was not enforced
  for session channels without an active subsystem, allowing a remote
  authenticated user to open an infinite number of channels and exhaust server
  resources despite the configured limit.

  The default value of the max_channels daemon option has been changed from
  infinity to 256. Deployments requiring more than 256 simultaneous channels per
  connection can restore the previous behavior by setting
  {max_channels, infinity}.

  The default value of the max_sessions daemon option has been changed from
  infinity to 1024. Deployments requiring more concurrent SSH connections can
  restore the previous behavior by setting {max_sessions, infinity}.

  Own Id: OTP-20287
  Application(s): ssh
  Related Id(s): GH-SA-qhcm-px9c-rvfh, PR-11523, CVE-2026-68956

asn1-5.3.4.3

The asn1-5.3.4.3 application can be applied independently of other applications
on a full OTP 27 installation.

Fixed Bugs and Malfunctions

• Fixed a denial-of-service attack in asn1, where abnormally large OID
  components (arcs) could cause resource exhaustion.

  Own Id: OTP-20272
  Related Id(s): PR-11655, CVE-2026-65634

• The JER backend will no longer break certain values (true, false, null) when
  they are typed as ENUMERATED, they will now be encoded as strings as required
  by the standard.

  Own Id: OTP-20355
  Related Id(s): ERIERL-1355, PR-11559

Full runtime dependencies of asn1-5.3.4.3

erts-14.0, kernel-9.0, stdlib-5.0

compiler-8.6.1.7

The compiler-8.6.1.7 application can be applied independently of other
applications on a full OTP 27 installation.

Fixed Bugs and Malfunctions

• In rare circumstances, the type analysis pass of the compiler could run for
  many minutes.

  Own Id: OTP-20365
  Related Id(s): GH-11534, PR-11566

• Certain uses of funs could crash the compiler. For example:

  f() ->
      F = fun Fn(0) -> 0; Fn(N) -> Fn(N - 1) end,
      [F(X) || X <- [1, 2]].
  

  This has been corrected.

  Own Id: OTP-20386
  Related Id(s): GH-11619, PR-11638

Full runtime dependencies of compiler-8.6.1.7

crypto-5.1, erts-13.0, kernel-8.4, stdlib-6.0

mnesia-4.23.5.5

The mnesia-4.23.5.5 application can be applied independently of other
applications on a full OTP 27 installation.

Fixed Bugs and Malfunctions

• Fixed mnesia:force_load_table/1 getting stuck when the remote node becomes
  unreachable during table loading. When a network loader is aborted due to
  sender node going down and a user has forced a table load, we now retry
  loading from disc instead. Additionally, for disc_only_copies tables, the
  process actually loading the table is the dets server process, not the mnesia
  loader, so it would not receive the abort notification and would hang
  indefinitely. Now it correctly receives the notification and aborts table
  loading.

  Own Id: OTP-20256
  Related Id(s): GH-11344, PR-11426

Full runtime dependencies of mnesia-4.23.5.5

erts-9.0, kernel-5.3, stdlib-5.0

public_key-1.17.1.6

The public_key-1.17.1.6 application can be applied independently of other
applications on a full OTP 27 installation.

Fixed Bugs and Malfunctions

• Align moduli and pubkey_moduli.hrl to state on OTP-28 and newer.

  Own Id: OTP-20367
  Related Id(s): PR-11574

Full runtime dependencies of public_key-1.17.1.6

asn1-5.0, crypto-5.0, erts-13.0, kernel-8.0, stdlib-4.0

ssh-5.2.11.13

The ssh-5.2.11.13 application can be applied independently of other applications
on a full OTP 27 installation.

Fixed Bugs and Malfunctions

• Fixed a vulnerability where the max_channels daemon option was not enforced
  for session channels without an active subsystem, allowing a remote
  authenticated user to open an infinite number of channels and exhaust server
  resources despite the configured limit.

  The default value of the max_channels daemon option has been changed from
  infinity to 256. Deployments requiring more than 256 simultaneous channels per
  connection can restore the previous behavior by setting
  {max_channels, infinity}.

  The default value of the max_sessions daemon option has been changed from
  infinity to 1024. Deployments requiring more concurrent SSH connections can
  restore the previous behavior by setting {max_sessions, infinity}.

  Own Id: OTP-20287
  Related Id(s): GH-SA-qhcm-px9c-rvfh, PR-11523, CVE-2026-68956

  *** POTENTIAL INCOMPATIBILITY ***

• The SSH daemon no longer rejects a subsystem request that is preceded by
  env or pty-req request on the same channel.

  Own Id: OTP-20371
  Related Id(s): ERIERL-1363, GH-11586, PR-11616

Full runtime dependencies of ssh-5.2.11.13

crypto-5.0, erts-14.0, kernel-9.0, public_key-1.6.1, runtime_tools-1.15.1,
stdlib-5.0, stdlib-6.0

ssl-11.2.12.13

Note! The ssl-11.2.12.13 application cannot be applied independently of other
applications on an arbitrary OTP 27 installation.

   On a full OTP 27 installation, also the following runtime
   dependency has to be satisfied:
   -- public_key-1.17.1.3 (first satisfied in OTP 27.3.4.12)

Fixed Bugs and Malfunctions

• Undecodable certificate_authorities names are now skipped, as they are just
  a hint.

  Own Id: OTP-20327
  Related Id(s): GH-11338, PR-11356

• Corrected generated keylog information generated from the keylog_hs option
  in the corner case that it was invoked after the client had reached its
  connection state, but the server closed the connection before it reached its
  connection state.

  Own Id: OTP-20358
  Related Id(s): ERIERL-1356, PR-11570

• Fix restart bug for TLS-1.3 session ticket server, introduced by backport
  commit in OTP-27.3.4.14, would case a restart to fail due to wrong number of
  arguments.

  Own Id: OTP-20384
  Related Id(s): PR-11632

• Reject unsolicited TLS-1.3 pre_shared_key in client.

  Own Id: OTP-20388
  Related Id(s): PR-11641, CVE-2026-89422

• Security and robustness hardening returning RFC mandated alert reasons,
  narrowing/correcting length checks.

  Correct signature algorithm handling that slightly mixed up signature
  algorithms and signature algorithms cert in TLS-1.2.

  Add missing TLS-1.3 Brainpool groups support. (Not relevant in 27 patch)

  Enhanced/corrected documentation and spec errors/deviations.

  Own Id: OTP-20390
  Related Id(s): PR-11651

Full runtime dependencies of ssl-11.2.12.13

crypto-5.1, erts-15.0, inets-5.10.7, kernel-9.0, public_key-1.17.1.3,
runtime_tools-1.15.1, stdlib-6.0

Thanks to

Alex Nogueira, ausimian

Original announcement: