CVE-2026-121808
Memory exhaustion via compressed Erlang terms in the elixir-grpc Erlpack codec
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.
Fixes and workarounds
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: EEFFix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: EEFFix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: EEFAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| grpc elixir-grpc grpc
hex |
≥ 0.4.0; < 1.0.0 (affected, semver)
Other versions: unaffected |
CNA: EEF |
| grpc elixir-grpc elixir-grpc/grpc
github |
≥ 25bcc569fe2cc4478531a6c546c923205fc751c9; < 0332faae5f5e132314794dbfdae5edecbccea292 (affected, git)
Other versions: unaffected |
CNA: EEF |
| grpc_core elixir-grpc grpc_core
hex |
≥ 1.0.0; < 1.1.0 (affected, semver)
Other versions: unaffected |
CNA: EEF |
| grpc_core elixir-grpc elixir-grpc/grpc
github |
≥ 0332faae5f5e132314794dbfdae5edecbccea292; < d6bc56ac75dfb6c02db2099909210a37c9be8db6 (affected, git)
Other versions: unaffected |
CNA: EEF |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 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 | CNA: EEF |
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-rqwpCNA: EEF · vendor-advisory, related
- https://cna.erlef.org/cves/CVE-2026-121808.htmlCNA: EEF · related
- https://osv.dev/vulnerability/EEF-CVE-2026-121808CNA: EEF · related
- https://github.com/elixir-grpc/grpc/commit/25bcc569fe2cc4478531a6c546c923205fc751c9CNA: EEF · related
- https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292CNA: EEF · patch
- https://github.com/elixir-grpc/grpc/commit/d6bc56ac75dfb6c02db2099909210a37c9be8db6CNA: EEF · patch
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