What is CVE-2026-3989?

CVE-2026-3989 is a high-severity vulnerability in Lmsys Sglang, classified under Deserialization of Untrusted Data. CVSS score: 7.8/10. Published 2026-03-12.

How severe is CVE-2026-3989?

High severity. CVSS v3 base score is 7.8 out of 10.

Deserialization in Lmsys Sglang

CVE-2026-3989

SGLangs `replay_request_dump.py` contains an insecure pickle.load() without validation and proper deserialization. An attacker can take advantage of this by providing a malicious .pkl file, which will execute the attackers code on the device running the script.

Vulnerability class: Insecure Deserialization

Published 2026-03-12 · last modified 2026-08-10.

CVSS v3 metric

CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (34.7th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 34.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.004 · change: -0.000

Affected products

Lmsys Sglang
Sglang — versions 0.5.10

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

github.com/sgl-project/sglang/blob/main/scripts/playground/replay_request_dump… (Product)
orca.security/resources/blog/sglang-llm-framework-rce-vulnerabilities/ (Exploit, Third Party Advisory)
github.com/sgl-project/sglang/releases/tag/v0.5.10 (Release Notes)
github.com/sgl-project/sglang/pull/20904 (Patch, Issue Tracking)

Frequently asked questions

What is CVE-2026-3989?: CVE-2026-3989 is a high-severity vulnerability in Lmsys Sglang, classified under Deserialization of Untrusted Data. CVSS score: 7.8/10. Published 2026-03-12.
How severe is CVE-2026-3989?: High severity. CVSS v3 base score is 7.8 out of 10.