OpenVPN v2.7.7

v2.7.7
Changed 1
  • Reduce number of future keys from 16 to 4 when using EPOCH data channel format
Fixed 7
  • Work around a pubkey-handling bug in mbedTLS 4.1.0 and 4.2.0
  • Prevent stale-routes-check from deleting permanent routes installed by --iroute and --ifconfig-push
  • Do not queue control ciphertext while a packet is still queued to fix TCP p2p handshake problems
  • Reenable xmit_hold when using p2p tcp-server and tls-server
  • Do not adjust UDP checksum if zero per RFC768
  • Avoid resetting the HMAC key on every packet with OpenSSL
  • Fix openvpnserv log lines format string on Windows to convert interface names with international characters from UTF8 to UCS16
Security 10
  • Avoid unbounded reliable TLS timeout in reliability layer and ignore acks for packets that cannot be outstanding
  • Fix CreateProcess() command line quoting for characters special to cmd.exe on Windows to prevent misbehavior with validation scripts and rogue CAs
  • Fix tapctl on Windows to always call netsh.exe with full path
  • Use proper DACL with system objects on Windows including service exit event and netsh.exe guard semaphore to prevent local DoS
  • Fix openvpnserv on Windows to pass correct NRPT domains size to prevent buffer overread with IDN domains using UTF8 encoding
  • Disallow '/' in config paths on Windows to prevent circumventing path validation

From OpenVPN

Security fixes:

  • reliability layer: avoid unbounded reliable TLS timeout, and ignore acks for packets that cannot be outstanding (CVE-2026-84732)

    Both reliability layer bugs found by Mark Bregman (Fox-IT)

  • windows: fix CreateProcess() command line quoting for characters that are special to cmd.exe, where a combination of validation script plus rogue CA could lead to misbehavior (CVE-2026-84256)

    Bug found by Clouditera Security

  • windows: fix tapctl to always call netsh.exe with full path (as we do elsewhere) (CVE-2026-84226)

    Bug found by BreachX Zero Day Labs (using Typhon AI Mil v2)

  • windows: don't use NULL DACL with system objects, namely the --service exit event and the netsh.exe guard semaphore.

    The old approach was prone to a local DoS where one user could interfere with other users' openvpn processes by blocking the netsh semaphore or sending events. This only affects setups not using the iservice, or using the automatic service to start/stop openvpn (CVE-2026-82312)

    Bug found by DEBRAJ BASAK

  • openvpnserv (windows): pass correct NRPT domains size - when IDN domains with UTF8 encoding were involved, a buffer overread could be achieved (CVE-2026-78221)

    Bug found by BreachX Zero Day Labs (using Typhon AI Mil v2)

  • openvpnserv (windows): don't allow '/' in config paths.

    The APIs windows uses for path validation do not handle '/' as path separator, while the file open APIs do, so this could be used to circumvent our config path validation, leading to openvpn.exe starting a user-controlled config file even if administratively not allowed (CVE-2026-78043)

    Bug found by BreachX Zero Day Labs (using Typhon AI Mil v2)

  • dhcp (windows): fix off-by-one in write_dhcp_search_str() temp buffer guard - suitable DHCP options could lead to a single-byte overflow of a temp buffer (CVE-2026-81738)

    Bug found by Andre Kropp (Nexory) and ChinhNguyen

  • linux netlink: validate netlink replies against the request

    Suggested by Joshua Rogers as a security improvement

  • openvpnserv (windows): fix off-by-one on input validation (discovered while fixing CVE-2026-78221)

  • openvpnserv (windows): harden CheckConfigPath() a bit more (another improvement while working on CVE-2026-78043)

User-visible Changes:

  • when using EPOCH data channel format, reduce the number of future keys from 16 to 4 - the previous calculation was wrong, and 4 spare keys are sufficient for 100+ Gbit/s links. This means less log spam in userland and fewer resources used in in-kernel implementations.
Bugfixes:

  • work around a pubkey-handling bug in mbedTLS 4.1.0 and 4.2.0 (supposedly fixed in 4.3.0)

  • multi: don't let stale-routes-check delete permanent routes - --stale-routes-check did not only delete dynamic cached routes, but also routes installed by --iroute and --ifconfig-push. Fixed by introducing route flags and restraining the check on them (Github: OpenVPN/openvpn#1063)

  • ssl: do not queue control ciphertext while a packet is still queued (fixes problems in TCP p2p handshake when both sides try to handshake at the same time) (Github: OpenVPN/openvpn#1089)

  • reenable xmit_hold when using p2p tcp-server and tls-server - in TCP server mode the server is not expected to initiate the TLS handshake. This was introduced by the multisocket code checking the wrong variable for socket protocol (Github: OpenVPN/openvpn#1089)

  • clinat: do not adjust UDP checksum if zero (as per RFC768) (Github: OpenVPN/openvpn#1037)

  • openssl: avoid resetting the HMAC key on every packet (Github: OpenVPN/openvpn#1088)

  • openvpnserv (windows): fix log lines format string - interface names with international characters printed in some error messages need to be converted from UTF8 to UCS16 first.

  • fix format string specifier for size_t (%zu)

  • fix test_misc compile issues with -Werror

Full Changelog: https://github.com/OpenVPN/openvpn/compare/v2.7.6...v2.7.7

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