# CVE-2025-3677: lm-sys fastchat apply_delta.py apply_delta_low_cpu_mem deserialization

> A local attacker can exploit unsafe deserialization in fastchat's apply_delta.py to execute arbitrary code.

- **Severity:** Medium 4.8 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 16 Apr 2025
- **Updated:** 21 Apr 2025
- **Also known as:** GHSA-v32v-5787-25w8

## What is CVE-2025-3677?

CVE-2025-3677 is a medium-severity unsafe deserialization vulnerability in lm-sys fastchat, published on 16 Apr 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability classified as critical was found in lm-sys fastchat up to 0.2.36. This vulnerability affects the function split_files/apply_delta_low_cpu_mem of the file fastchat/model/apply_delta.py. The manipulation leads to deserialization. An attack has to be approached locally.

Weakness: CWE-502 (Deserialization of Untrusted Data), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2025-3677?


## How do I fix CVE-2025-3677?

No fix has been published for CVE-2025-3677 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-3677 being exploited?

There is no known exploitation of CVE-2025-3677 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-3677 and fix it if it is affected.

What it is: CVE-2025-3677 is a medium-severity unsafe deserialization vulnerability in lm-sys fastchat, published on 16 Apr 2025. 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-2025-3677 in the wild and no public exploit code.

Affected product: lm-sys fastchat. 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-2025-3677/ (Markdown: https://insights.sbomify.com/CVE-2025-3677/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-3677
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-3677
- OSV: https://osv.dev/vulnerability/CVE-2025-3677

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From sbomify Insights: https://insights.sbomify.com/CVE-2025-3677/
Summaries are generated and may contain mistakes; the official description above is the record.