# CVE-2026-55737: Heap pointer corruption via signed/unsigned mismatch in LARGE_TUPLE_EXT decoding in erts external term format decoder

> An attacker can crash the Erlang VM by sending a crafted external term format binary that triggers a signed/unsigned mismatch in tuple decoding.

- **Severity:** Medium 5.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Jul 2026
- **Updated:** 28 Jul 2026
- **Also known as:** AZL-94208, DEBIAN-CVE-2026-55737, EEF-CVE-2026-55737, GHSA-446w-268v-9462, UBUNTU-CVE-2026-55737

## What is CVE-2026-55737?

CVE-2026-55737 is a medium-severity vulnerability in Erlang OTP, published on 27 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### 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.

Weakness: CWE-787 (Out-of-bounds Write), CWE-195 (Signed to Unsigned Conversion Error)

## Which versions are affected by CVE-2026-55737?

It affects 2 products.


Products: Erlang Erlang\/Otp, Erlang Erts.

## How do I fix CVE-2026-55737?

Upgrade to a fixed version.

## Is CVE-2026-55737 being exploited?

There is no known exploitation of CVE-2026-55737 in the wild and no public exploit code.

## Other vulnerabilities in Erlang OTP

- [CVE-2022-37026](https://insights.sbomify.com/CVE-2022-37026/): Auth bypass in n/a (critical 9.8)
- [CVE-2016-10253](https://insights.sbomify.com/CVE-2016-10253/): Memory corruption in n/a (critical 9.8)
- [CVE-2026-55953](https://insights.sbomify.com/CVE-2026-55953/): TLS 1.2 and DTLS client accepts unoffered anonymous cipher suite, bypassing server authentication (critical 9.1)
- [CVE-2026-49759](https://insights.sbomify.com/CVE-2026-49759/): Stack buffer overflow in SCTP error cause parsing in inet_drv allows remote VM crash (high 8.8)
- [CVE-2026-58227](https://insights.sbomify.com/CVE-2026-58227/): TLS/DTLS denial of service via unbounded recursion on cross-signed peer certificate chain (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55737 and fix it if it is affected.

What it is: CVE-2026-55737 is a medium-severity vulnerability in Erlang OTP, published on 27 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-55737 in the wild and no public exploit code.

Affected product: Erlang OTP. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55737/ (Markdown: https://insights.sbomify.com/CVE-2026-55737/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55737
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55737
- OSV: https://osv.dev/vulnerability/CVE-2026-55737

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55737/
Summaries are generated and may contain mistakes; the official description above is the record.