CVE-2026-55737 in OTP
Summary
by MITRE • 07/27/2026
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.
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Analysis
by VulDB Data Team • 07/27/2026
This vulnerability represents a critical heap corruption flaw in Erlang OTP's BEAM virtual machine that stems from inconsistent signedness handling during ETF binary decoding operations. The issue manifests when processing LARGE_TUPLE_EXT terms where the validation phase reads a 32-bit arity field as unsigned using get_uint32() while the decoding phase subsequently interprets the same field as signed using get_int32() into a C int type. This fundamental mismatch creates a scenario where an arity value of 0x80000000 passes validation as 2147483648 but gets decoded as -2147483648 due to two's complement representation, causing the heap pointer to move backwards during allocation. The vulnerability operates under CWE-190, specifically addressing integer overflow conditions that occur when converting from one integer type to another with different signedness properties, and aligns with ATT&CK technique T1203 for process injection through malformed data processing.
The technical execution requires an attacker to craft a malicious ETF binary containing a LARGE_TUPLE_EXT term with the specific arity value of 0x80000000, which bypasses validation checks while triggering the signedness conversion error during decoding. The absence of runtime tuple-arity limit enforcement through MAX_ARITYVAL further exacerbates the issue by allowing arbitrary large values to proceed unchecked. When the heap pointer moves backward due to the negative calculated value, subsequent memory operations result in out-of-bounds heap writes that corrupt the virtual machine's internal state. This corruption manifests as an impossible heap size detection followed by VM termination, effectively causing a denial of service condition that impacts all applications running on affected OTP versions.
The operational impact extends beyond simple service disruption to encompass potential system stability risks and application reliability concerns in environments where Erlang-based systems process untrusted ETF data streams. Attackers can exploit this vulnerability through any interface that accepts ETF binary data, including network protocols, file parsing operations, or inter-process communication mechanisms that utilize the binary_to_term/1 function. The vulnerability affects OTP versions from 25.0 through 28.5.0.4 and 29.0.4, encompassing multiple major releases and requiring careful version management across deployment environments. Organizations should prioritize patching to versions 27.3.4.15, 28.5.0.4, and 29.0.4 which contain the necessary fixes for erts versions 13.0 through 17.0.4, as these releases address both the signedness conversion error and the missing tuple-arity validation checks that together enable the heap corruption scenario.
Mitigation strategies should include immediate deployment of patched OTP versions across all affected systems while implementing additional input validation measures for ETF data sources. Organizations should also consider network-level filtering to prevent untrusted ETF data from reaching critical Erlang applications, particularly in scenarios involving external data processing or network communication. The vulnerability demonstrates the importance of consistent type handling and proper bounds checking in low-level virtual machine implementations, highlighting how seemingly minor signedness mismatches can lead to serious security implications in systems processing structured binary formats. System administrators should monitor for any signs of attempted exploitation through unexpected VM crashes or restarts in environments processing ETF data from untrusted sources, as the denial of service aspect makes this vulnerability particularly attractive for attackers seeking to disrupt Erlang-based services.