v3.2.0

libmodbus 3.2.0 (2026-07-02)

• Add modbus_proxy() to bridge two Modbus backends (closes #70).
• Add termios2 support to allow custom baud rates (RTU).
• Return an exception response for READ EXCEPTION STATUS (0x07).
• Use EMBXILVAL instead of EMBMDATA for illegal data value errors.
• modbus_reply: reject NULL req and mb_mapping arguments.
• modbus_reply: validate request length before reading per-function fields.
• Fix signed integer overflow in modbus_get_float_*() (reported by Dominik
  Blain and Henrik Brodin).
• Fix signed integer overflow in the MODBUS_GET_INT*_FROM_INT* macros;
  MODBUS_GET_INT16_FROM_INT8() now returns a signed int16_t in every context
  (reported by Henrik Brodin - Trail of Bits).
• Fix strict aliasing violation in modbus_set_float_*() by using memcpy
  (reported by Henrik Brodin).
• Remove dead code (Coverity CID 561619).
• modbus-rtu: don't use O_EXCL when opening the device (#760).
• WIN32 compatibility for setsockopt() in modbus-tcp.c (#800).
• Check if ai_list is null before freeing it (#831).
• Respect user-provided CFLAGS (closes #836).
• Fix test to use ctx instead of invalid_ctx (closes #791, #792).
• Update documentation of float functions (closes #838).
• Fix documentation examples of modbus_get_float_* functions.
• modbus_reply_exception: reject a NULL request pointer.
• modbus_mask_write_register: validate that ctx is not NULL.
• modbus_write_and_read_registers: validate src/dest pointers and counts.
• modbus_report_slave_id: reject a NULL dest buffer.
• modbus_get_*_timeout: validate that the output pointers are not NULL.
• modbus_mapping_new_start_address: cap table dimensions.
• modbus_mapping_new: reject negative counts.
• modbus_rtu_set_custom_rts: reject a NULL callback.
• modbus-rtu: avoid integer overflow in the RTS post-send delay.
• modbus-rtu: check the return values of the RTS ioctl calls.
• modbus-rtu: check the return value when saving termios settings on connect.
• modbus-rtu: report a failure to restore termios settings on close.
• modbus_new_rtu: reject negative baud rates.
• modbus-tcp: guard freeaddrinfo() against NULL on resolver failure.
• modbus_new_tcp: NUL-terminate the IP string when ip is NULL.
• modbus_reply: validate FC22 request length before writing the register.
• modbus-tcp: keep ctx->s consistent across failed or repeated connects (no
  false success on a stale descriptor, no socket leak on reconnect).
• modbus-tcp: don't override the user error recovery mode in the flush overflow
  path.
• modbus-tcp: fully initialize the sigaction struct for the SIGPIPE handler on
  BSD.
• modbus-rtu: fix the Windows serial handle lifecycle (initialize the handle,
  guard close against a never-opened handle and reset it after close).
• modbus-rtu: sleep the RTS turnaround delay in chunks to stay portable with
  usleep().
• modbus_new_rtu: validate data_bit and stop_bit arguments.
• modbus_send_raw_request_tid: reject NULL raw_req with EINVAL.
• modbus_get_byte_from_bits: remove an always-false assert and clamp nb_bits
  consistently in debug and release builds.
• Preserve errno across the Windows error-recovery paths.
• tests: don't kill the unit test server on RTU bad-CRC frames.
• tests: fix integer overflow in the bandwidth-client rate computation.

New Contributors

• @micrictor made their first contribution in #831
• @desteemy made their first contribution in #800

Full Changelog: v3.1.12...v3.2.0

v3.1.12

What's Changed

• Fix FD_SET overflow when socket fd >= FD_SETSIZE.
• Check dest pointer not null and nb in read functions.
• NULL check for src and nb < 1 validation in write functions.
• modbus_reply: don't compute address for FC 0x07/0x11.
• Use O_NONBLOCK instead of deprecated O_NDELAY (closes #710).
• Explicit cast for Coverity CID 416366.
• Document required buffer size of modbus_receive.
• Document macros for error codes corresponding to Modbus exceptions (#758).
• Fix example of modbus_rtu_set_serial_mode (closes #552).
• Test filesystem provides symlink in autogen.sh (closes #414).
• Sync API signatures with the documentation.
• Many documentation fixes and typo corrections.
• Add coverage target and helper script.

New Contributors

• @kyllingstad made their first contribution in #758

Full Changelog: v3.1.11...v3.1.12

v3.1.11

What's Changed

• RTU - Check CRC before filtering on slave ID
• HAVE_NETINET_IN_H as guard around header (closes #765)
• Use default port 502 in documentation.
• Fix float endianness issue introduced in v3.1.8 (49af73d). Thank you @ghorwin for your excellent work on the subject. Closes #665, #694, #757, #770.
• Proper display of used CFLAGS.
• Don't build with debug flag by default anymore.
• Check request length in modbus_reply when used in memcpy.
  Thank you Nozomi Networks Labs Advisory for the report.
• Fix insecure data handling. CID 416366: INTEGER_OVERFLOW found with Coverity Scan.
• Remove useless cast in setsockopt call (closes #721)
• Link against socket and nsl libs when building on SunOS. Thank you @lanurmi.
• Update documentation about tcp-pi requiring 1 KiB of extra memory (closes #715). Thank you @psychon.
• Documentation improvements by @cedricboudinet and @mhei.
• Revert TCP checks for recovery (closes #711).
• Don't use loop initial declaration (closes #752).
• Fix wrong generated version for double number in win32 (closes #675).
• Don't use gai_strerror if not available.
• Add checks for netinet/ip.h and gai_strerror (#745)
• Log error in read input registers if debug (closes #755).
• Fix errno value on timeout with TCP connect (closes #736, #756).
  Thank you @kyllingstad for the issue and @psychon for the fix.
• Free addrinfo struct on getaddrinfo() gerrors.
• Fix doc of modbus_mapping_new_start_address (#615).

New Contributors

• @yauyimsing made their first contribution in #702
• @cedricboudinet made their first contribution in #682
• @lanurmi made their first contribution in #398
• @ghorwin made their first contribution in #694
• @diplfranzhoepfinger made their first contribution in #765

Full Changelog: v3.1.10...v3.1.11

v3.1.10

Urgent release to fix a regression.

• Fix baud rate handling with RTU under Linux
• Fix modbus_disable_quirks signature

v3.1.9

What's Changed

• Remove Travis CI
• Move content about migration to libmodbus.org
• Avoid negative value in FD_SET call
• Test socket against positive value instead of -1
• Improvements to autotools by @ndim
• Fix doc links by @jordanjohnson56 (#653)
• Test the protocol id for 0 by @metapsychologe (#509)
• Fix double negative in tests
• New quirks handler (closes #38 #533)
• Fix bitwise OR in documentation
• Improve doc about slave ID in RTU
• Add .clang-format and format code (closes #394)
• Remove constraints on baud rate values
• Accept IP or device in arg of unit test progs
• Avoid compilation issue with VS2022 with strdup
• Display created files in configure.js
• Use strcpy_s under Windows
• Replace inet_addr by inet_pton calls
• Replace inet_ntoa by inet_ptop
• Update configure.ac/config.h.win32 for new inet functions
• Instructions to build libmodbus in a VS project
• Fix connection check for Windows RTU (closes #660, #662)
• Add CIFuzz Github action by @DavidKorczynski (#669)
• Convert a few int to unsigned int (#402)

New Contributors

• @jordanjohnson56 made their first contribution in #653
• @metapsychologe made their first contribution in #509
• @DavidKorczynski made their first contribution in #669

v3.1.8

• Major rewrite of documentation with Material for mkdocs
• Reduce memory use of TCP PI backend (closes #621)
• Fixed MODBUS_ERROR_RECOVERY_LINK not working on Windows (@embeddedmz)
• Replace Travis CI by GitHub CI
• Fix linker error for Windows (VCLinkerTool)
• Address check in single register / coil responses added (#463)
• Swap CRC bytes in request data but not at CRC computing (#397)
• Fix float endianness issue on big endian architecture
• Fix comment about EMBUNKEXC (closes #566)
• Fix network library detection on Haiku
• Fix typos (closes #620)

New Contributors

• @JetForMe made their first contribution in #624
• @Begasus made their first contribution in #622
• @ndunks made their first contribution in #616
• @bachp made their first contribution in #463
• @alongL made their first contribution in #631
• @embeddedmz made their first contribution in #644

Full Changelog: v3.1.7...v3.1.8

v3.1.7

What's Changed

• SPDX: change LGPL-2.1+ to LGPL-2.1-or-later by @yegorich in #489
• fix MODBUS_GET_* macros in case of negative values by @i-ky in #441
• docs: fix simple typo, reponse -> response by @timgates42 in #569
• Update README.md by @anton-bondarev in #580
• Install NEWS and AUTHORS files with library, ship LICENSE with tests by @richardash1981 in #545
• minor typo by @stefannilsson in #539
• cosmetic changes in man page standardizing itemization by @Zugschlus in #460
• modbus_reply: fix copy & paste error in sanity check (fixes #614) by @mhei in #619
• add SECURITY.md (closes #613)
• fix typo in comment (closes #588)
• replace obsolete AC_PROG_CC_STDC by AC_PROG_CC
• fix position of CC flags in documentation (closes #599)
• remove duplicate ';' (closes #602)
• add the baud rate of 256k for Windows (closes #603)
• replace .dir-locals.el (Emacs) by .editorconfig
• move malloc before starting unit tests

All changes w/o attribution by @stephane.

New Contributors

• @i-ky made their first contribution in #441
• @timgates42 made their first contribution in #569
• @anton-bondarev made their first contribution in #580
• @richardash1981 made their first contribution in #545
• @stefannilsson made their first contribution in #539
• @Zugschlus made their first contribution in #460

Full Changelog: v3.1.6...v3.1.7

v3.1.6

• Fix awful typo in fix for VD-1301 vulnerability.
  Thank you @karlp.

v3.0.8

• Fix awful typo in fix for VD-1301 vulnerability.
  Thank you @karlp.

v3.1.5

• Add appveyor.com config
• Change arg value from int to const uint16_t in modbus_write_register
• Mark raw_req argument as const in modbus_send_raw_request (closes #479)
• Add unit tests for VD-1301 and VD-1302 vulnerabilities
• Fix VD-1301 and VD-1302 vulnerabilities
• Create CODE_OF_CONDUCT.md
• modbus_mapping_t is now a named typedef (to allow forward declaration)
• Rename type as flags for consistency between functions
• Add missing SOCK_CLOEXEC flag on socket creation
• Remove wrong and harmful checks in configure.ac
• Oops fix OR on RS485 settings (1c5d969)
• Only set SER_RS485_ENABLED bit of existing RS485 settings
• Add .vscode/ to .gitignore
• Fix wrong function name
• Remove a duplicated semi-colon
• Fix a small typo in test message
• Fix modbus_reply for TCP when unit id == 0 (fixes #376)
• New functions to define the indication timeout (#95)
• Remove CYGWIN condition to provide bswap16 fallback (#383)
• Use builtin bswap16 of gcc 4.8 (#377)
• Handle out-of-memory conditions more gracefully
• Add entry points for accept/listen in libmodbus index
• Refine issue template for Github
• Move WINVER definition before other includes (#350)
• Add new function modbus_get_slave()
• Fix LIBMODBUS_VERSION_HEX encoding (closes #345)
• tcp_modbus_accept mustn't close socket on error (closes #333)