What is CVE-2021-35331?

CVE-2021-35331 is a high-severity vulnerability in Tcl, classified under Use of Externally-Controlled Format String. CVSS score: 7.8/10. Published 2021-07-05.

How severe is CVE-2021-35331?

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

Vulnerability in Tcl

CVE-2021-35331

In Tcl 8.6.11, a format string vulnerability in nmakehlp.c might allow code execution via a crafted file. NOTE: multiple third parties dispute the significance of this finding

Published 2021-07-05 · last modified 2026-06-17.

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: 0.016 (75.4th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 75th percentile — 75.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.016 · newest: 0.016 · change: 0.000

Affected products

Tcl — versions 8.6.11

Weakness classification (CWE)

CWE-134 — Use of Externally-Controlled Format String

References

core.tcl-lang.org/tcl/info/bad6cc213dfe8280 (Exploit, Vendor Advisory)
core.tcl-lang.org/tcl/info/28ef6c0c741408a2 (Exploit, Patch, Vendor Advisory)
github.com/tcltk/tcl/commit/4705dbdde2f32ff90420765cd93e7ac71d81a222 (Patch, Third Party Advisory)
sqlite.org/forum/info/7dcd751996c93ec9 (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-35331?: CVE-2021-35331 is a high-severity vulnerability in Tcl, classified under Use of Externally-Controlled Format String. CVSS score: 7.8/10. Published 2021-07-05.
How severe is CVE-2021-35331?: High severity. CVSS v3 base score is 7.8 out of 10.