# CVE-2026-121808: Memory exhaustion via compressed Erlang terms in the elixir-grpc Erlpack codec

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in elixir-grpc grpc_core and grpc allows unauthenticated attackers to exhaust server memory via a compressed Erlang external term in a gRPC message body.

GRPC.Codec.Erlpack.decode/2 (grpc_core/lib/grpc/codec/erlpack.ex, and lib/grpc/codec/erlpack.ex before the package split) passes the message body to :erlang.binary_to_term/2. That function inflates a compressed term in full before it returns. The codec sets no limit on the decoded size, and its type checks run only on the decoded term. The server's max_body_size limit counts the compressed bytes of the request. A request with Content-Type: application/grpc+erlpack can therefore make the server allocate a term much larger than the request body.

This issue affects grpc: from 0.4.0 before 1.0.0; grpc_core: from 1.0.0 before 1.1.0.

## Remediation

- workaround: Remove GRPC.Codec.Erlpack from the server's codecs list if the codec is not needed.

If the codec is needed, register a wrapper codec in its place. The wrapper implements the GRPC.Codec behaviour, returns "erlpack" from name/0, raises in decode/2 when the body starts with the bytes 131, 80 (the compressed term tag), and delegates all other calls to GRPC.Codec.Erlpack. (source: CNA: EEF)
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292
- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: EEF) — https://github.com/elixir-grpc/grpc/commit/d6bc56ac75dfb6c02db2099909210a37c9be8db6

## Affected products and versions

- elixir-grpc / grpc (grpc): ≥ 0.4.0; < 1.0.0 (affected, semver). Source: CNA: EEF
- elixir-grpc / grpc (elixir-grpc/grpc): ≥ 25bcc569fe2cc4478531a6c546c923205fc751c9; < 0332faae5f5e132314794dbfdae5edecbccea292 (affected, git). Source: CNA: EEF
- elixir-grpc / grpc_core (grpc_core): ≥ 1.0.0; < 1.1.0 (affected, semver). Source: CNA: EEF
- elixir-grpc / grpc_core (elixir-grpc/grpc): ≥ 0332faae5f5e132314794dbfdae5edecbccea292; < d6bc56ac75dfb6c02db2099909210a37c9be8db6 (affected, git). Source: CNA: EEF

## Severity and prioritization

- CVSS 4.0: 8.2 (high); CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N; source: CNA: EEF

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-409

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xxp9-7hp4-rqwp (CNA: EEF; vendor-advisory, related)

- https://cna.erlef.org/cves/CVE-2026-121808.html (CNA: EEF; related)

- https://osv.dev/vulnerability/EEF-CVE-2026-121808 (CNA: EEF; related)

- https://github.com/elixir-grpc/grpc/commit/25bcc569fe2cc4478531a6c546c923205fc751c9 (CNA: EEF; related)

- https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292 (CNA: EEF; patch)

- https://github.com/elixir-grpc/grpc/commit/d6bc56ac75dfb6c02db2099909210a37c9be8db6 (CNA: EEF; patch)

## Provenance

- CNA: EEF: https://www.cve.org/CVERecord?id=CVE-2026-121808; retrieved 2026-11-13; source updated 2026-11-13

Revision: 6a798f7c94d2442cec355a368b96d7be1598b161de5a0163b4857943b478ce9d

Canonical: https://y2.dev/cve/CVE-2026-121808

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