Erlang OTP prior 27.3.4.15/28.5.0.4/29.0.4 External Term Format Decoder external.c decoded_size out-of-bounds write

Summaryinfo

A vulnerability classified as problematic was found in Erlang OTP. This vulnerability affects the function decoded_size of the file erts/emulator/beam/external.c of the component External Term Format Decoder. Such manipulation leads to out-of-bounds write. This vulnerability is traded as CVE-2026-55737. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Erlang OTP. Affected by this issue is the function decoded_size of the file erts/emulator/beam/external.c of the component External Term Format Decoder. The manipulation with an unknown input leads to a out-of-bounds write vulnerability. Using CWE to declare the problem leads to CWE-787. The product writes data past the end, or before the beginning, of the intended buffer. Impacted is availability. CVE summarizes:

Signed to Unsigned Conversion Error and Out-of-bounds Write vulnerability in Erlang OTP erts allows an attacker who can supply a crafted Erlang external term format (ETF) binary to binary_to_term/1 to corrupt the BEAM heap pointer and crash the virtual machine. When decoding a LARGE_TUPLE_EXT term, the validation pass decoded_size() in erts/emulator/beam/external.c reads the 32-bit arity field as unsigned (get_uint32()), while the decode pass dec_term() reads the same field as a signed 32-bit integer (get_int32()) into an int. An arity wire value of 0x80000000 passes validation as 2147483648 but decodes as -2147483648, so the subsequent hp += n moves the heap allocation pointer backward. Neither pass enforces the runtime tuple-arity limit MAX_ARITYVAL. The result is an out-of-bounds heap write; in practice the VM detects an impossible heap size and aborts, denying service. The required padding is large when uncompressed but the compressed-ETF envelope shrinks it to a small payload on the wire. This issue affects OTP from OTP 25.0 before 27.3.4.15, 28.5.0.4, and 29.0.4 corresponding to erts from 13.0 before 15.2.7.11, 16.4.0.4, and 17.0.4.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-55737 since 06/17/2026. The exploitation is known to be easy. The attack may be launched remotely. Technical details are known, but there is no available exploit.

Upgrading to version 27.3.4.15, 28.5.0.4 or 29.0.4 eliminates this vulnerability.

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Productinfo

Vendor

• Erlang

Name

• OTP

Website

• Product: https://github.com/erlang/otp/

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