8.7

CVE-2026-115349: Mistune 3.0.0 before 3.3.0 Denial of Service via Nested Bracket Parsing

Deferred
AliasesDEBIAN-CVE-2026-115349UBUNTU-CVE-2026-115349
Published 22-10-2026Last modified 26-10-2026

Vulnerability summary

CVE-2026-115349 is a high (CVSS 8.7) vulnerability in lepture mistune. EPSS estimates a 0.34% chance of exploitation in the next 30 days, higher than 27.9% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 8.7 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 0% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
8.7/10
010
High · v4.0 (CVE.org)
EPSS score
0.34%
0%100%
Low · Change unavailable
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Timeline

  1. 22-10-2026
    PublishedVulnerability first disclosed.
  2. 26-10-2026
    Last modifiedVulnerability information updated.

Description

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.

CVSS metrics

7 scores · 4 sources · 2 versions

EPSS trend

Probability

0.34%

Chance of exploitation in the next 30 days

Percentile

28%

Versus all other CVEs

30-day change

Change unavailable

Change unavailable

23-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Debian1 product
  • mistuneAll versions (No fix recorded)
Lepture1 product
Ubuntu1 product
  • mistuneAll versions (No fix recorded)

3 vendors · 3 products

References

5 links