Vulnerability · Published Jul 27, 2026 · Assigned by EEF
CVE-2026-55737Heap pointer corruption via signed/unsigned mismatch in LARGE_TUPLE_EXT decoding in erts external term format decoder
Medium 5.1
In plain English
A medium-severity out-of-bounds write in OTP from Erlang. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | erlang | no fix listed | DEBIAN-CVE-2026-55737 |
| Debian:13 | erlang | 1:27.3.4.1+dfsg-1+deb13u3 | DEBIAN-CVE-2026-55737 |
| Debian:14 | erlang | 1:29.0.4+dfsg-1 | DEBIAN-CVE-2026-55737 |
| Ubuntu:22.04:LTS | erlang | 1:24.2.1+dfsg-1ubuntu0.7 | USN-8827-1 |
| Ubuntu:24.04:LTS | erlang | 1:25.3.2.8+dfsg-1ubuntu4.7 | UBUNTU-CVE-2026-55737 |
| Ubuntu:24.04:LTS | erlang | 1:25.3.2.8+dfsg-1ubuntu4.7 | USN-8827-1 |
| Ubuntu:26.04:LTS | erlang | 1:27.3.4.6+dfsg-1ubuntu0.1 | USN-8827-1 |
| Ubuntu:26.04:LTS | erlang | 1:27.3.4.6+dfsg-1ubuntu0.1 | UBUNTU-CVE-2026-55737 |
Affected products (as reported)
Weakness: CWE-195, CWE-787 · Vector: 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
References
- https://github.com/erlang/otp/security/advisories/GHSA-446w-268v-9462 vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-55737.html related
- https://osv.dev/vulnerability/EEF-CVE-2026-55737 related
- https://www.erlang.org/doc/system/versions.html#order-of-versions x_version-scheme
- https://github.com/erlang/otp/commit/c5210b42a9d3d96f3d25601942ce8122be0f3761 patch