lm-sys fastchat apply_delta.py apply_delta_low_cpu_mem deserialization

published 2025-04-16 18 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-11794

cvss: 5.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 10%
public exploits: 0; none known

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.

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 18 mo ago (2025-04-16)

Exploit prediction

0.21% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	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
CNA	3.1	5.3	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
CNA	3.0	5.3	CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
CNA	2.0	4.3	AV:L/AC:L/Au:S/C:P/I:P/A:P
CNA	4.0	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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

lm-sys fastchat

Classification

Weakness

CWE-502 Deserialization of Untrusted Data
CWE-20 Improper Input Validation

References

vuldb.com /?id.304966
vdb-entry, technical-description
vuldb.com /?ctiid.304966
signature, permissions-required
vuldb.com /?submit.552755
third-party-advisory
github.com /lm-sys/FastChat/issues/3713
issue-tracking

Sources

CVE List CVE-2025-3677
NVD CVE-2025-3677

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary