# GHSA-v2jf-442r-6mjh: nebula-mesh: Signed-poll nonce LRU is in-memory and bounded; replay survives restart + eviction

> Attackers can replay signed-poll requests after server restarts or cache eviction to steal enrollment tokens and compromise agent identities.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Jun 2026
- **Also known as:** GO-2026-5815

## What is GHSA-v2jf-442r-6mjh?

GHSA-v2jf-442r-6mjh is a vulnerability in github.com/juev/nebula-mesh, published on 26 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

`internal/api/pop/nonce.go:25,40,86` + `internal/api/server.go:38` — the signed-poll nonce cache is an in-process LRU sized at 65,536 entries. `internal/api/updates.go:31` sets `pollClockSkew = 5 * time.Minute` as the replay window.

## Affected
All released versions through v0.3.0 that have shipped the ADR 0004 signed-poll path. (If this is gated behind a feature flag, on a side branch, or not yet on a release tag, please flag — this advisory may not apply to the released artifact yet.)

## Threat model
A captured signed-poll request can be replayed:

1. **After any process restart** — the in-memory LRU is wiped, so the original nonce becomes "unseen" again. Replay succeeds if the original timestamp is still within the 5-minute skew.
2. **After forced eviction** — an attacker with control of any single host can flood >65,536 nonces under their own host_id, driving the global LRU to evict the victim's recorded nonce. Replay then succeeds.

Impact is bounded: a replayed poll fetches the `/api/v1/agent/updates` body. That body can include a freshly-minted enrollment token if a rekey is pending (`updates.go:249-260`) — at which point the attacker holds a single-use token they can redeem under their own keypair.

## Suggested fix
Two options, either acceptable:

1. Persist nonces in SQLite keyed by `(host_id, nonce)` with `ON CONFLICT DO NOTHING`, retained for the timestamp-skew window. Adds one transactional INSERT per poll; bounded by the skew window (~5 min worth of rows server-wide).
2. Per-host cap on the LRU instead of a global 65k cap, so one host cannot evict another's records. Combined with shorter skew (≤30s) to bound the post-restart replay window.

Option 1 is more robust; option 2 is lower-implementation-effort.

## Which versions are affected by GHSA-v2jf-442r-6mjh?

3 open source packages ship an affected version, including github.com/juev/nebula-mesh.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/juev/nebula-mesh` | Go | All versions | 0.3.4 |
| `github.com/juev/nebula-mesh` | Go | All versions | 0.3.4 |
| `github.com/juev/nebula-mesh` | Go | All versions | 0.3.4 |

## How do I fix GHSA-v2jf-442r-6mjh?

Upgrade github.com/juev/nebula-mesh to 0.3.4 or later.

## Is GHSA-v2jf-442r-6mjh being exploited?

There is no known exploitation of GHSA-v2jf-442r-6mjh in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-v2jf-442r-6mjh and fix it if it is affected.

What it is: GHSA-v2jf-442r-6mjh is a vulnerability in github.com/juev/nebula-mesh, published on 26 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-v2jf-442r-6mjh in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/juev/nebula-mesh (Go): affected all versions; fixed in 0.3.4
- github.com/juev/nebula-mesh (Go): affected all versions; fixed in 0.3.4
- github.com/juev/nebula-mesh (Go): affected all versions; fixed in 0.3.4

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/GHSA-v2jf-442r-6mjh/ (Markdown: https://insights.sbomify.com/GHSA-v2jf-442r-6mjh/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-v2jf-442r-6mjh

---
From sbomify Insights: https://insights.sbomify.com/GHSA-v2jf-442r-6mjh/
Summaries are generated and may contain mistakes; the official description above is the record.