Heap pointer corruption via signed/unsigned mismatch in LARGE_TUPLE_EXT decoding in erts external term format decoder

Weakness Type (CWE)

CWE-195 — CWE-195 Signed to Unsigned Conversion Error

CAPEC

CAPEC-92 — CAPEC-92 Forced Integer Overflow

CVSS 4.0 Score

5.1

MEDIUM

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Vulnerability description

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 OTP 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15, corresponding to erts from 13.0 before 17.0.4, 16.4.0.4 and 15.2.7.11.

Affected

`pkg:otp/erts`

Module	Source File	Routine
`erlang`	`emulator/beam/external.c`	`erlang:binary_to_term/1`
`external`		`erlang:binary_to_term/2`
		`dec_term`
		`decoded_size`

Status	Type	Version	Changes / Fixed in
affected	otp ^ⓘ	`13.0`	unaffected at `17.0.4` unaffected at `16.4.0.4` unaffected at `15.2.7.11`

`pkg:github/erlang/otp`

Module	Source File	Routine
`erlang`	`erts/emulator/beam/external.c`	`erlang:binary_to_term/1`
`external`		`erlang:binary_to_term/2`
		`dec_term`
		`decoded_size`

Status	Type	Version	Changes / Fixed in
affected	otp ^ⓘ	`25.0`	unaffected at `29.0.4` unaffected at `28.5.0.4` unaffected at `27.3.4.15`
affected	git ^ⓘ	`ebcbb97b4e`	< `c5210b42a9`

References

https://github.com/erlang/otp/security/advisories/GHSA-446w-268v-9462 vendor-advisory related
https://osv.dev/vulnerability/EEF-CVE-2026-55737 related
https://github.com/erlang/otp/commit/c5210b42a9d3d96f3d25601942ce8122be0f3761 patch

Credits

Finder: Nick Gunn
Remediation developer: Kiko Fernandez-Reyes
Remediation reviewer: Sverker Eriksson

CVE record as JSON: GET /cves/CVE-2026-55737.json
OSV record as JSON: GET /osv/EEF-CVE-2026-55737.json