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CVE-2026-115348

Mistune before 3.3.0 Quadratic-Time DoS via parse_link_text

8.7 High

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

0.44%Up 0.1 points since Oct 23, 2026
90%50%10%1%

What each source reports

CVE List Score used 8.7

Mistune before 3.3.0 Quadratic-Time DoS via parse_link_text

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Record
CVE-2026-115348
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
EUVDEUVD-2026-108417 8.7

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Record
EUVD-2026-108417
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-h98w-84rc-h77q 8.7

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline...

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Record
GHSA-h98w-84rc-h77q
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
NVD 8.7

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Record
CVE-2026-115348
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-400
Updated
2026-11-02
OSV 8.7

Mistune before 3.3.0 Quadratic-Time DoS via parse_link_text

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Record
CVE-2026-115348
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Weakness
CWE-400
Updated
2026-11-04
OSVDEBIAN-CVE-2026-115348 8.7

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Record
DEBIAN-CVE-2026-115348
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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
Updated
2026-11-02
OSVUBUNTU-CVE-2026-115348 8.7

Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.

Record
UBUNTU-CVE-2026-115348
CVSS 4.0
8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVopenSUSE-SU-2026:12407-1 No score

python313-mistune-3.4.0-2.1 on GA media

These are all security issues fixed in the python313-mistune-3.4.0-2.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:12407-1
Updated
2026-11-04

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mistune
Debian:12
 All versions, plus listed versions
2.0.4-12.0.4-23.0.2-13.0.2-23.1.3-13.1.4-13.3.4-13.4.0-1
 None known
mistune
Debian:13
 All versions, plus listed versions
3.1.3-13.1.4-13.3.4-13.4.0-1
 None known
mistune
Debian:14
 All versions, plus listed versions
3.1.3-13.1.4-13.3.4-13.4.0-1
 None known
mistune
Ubuntu:16.04:LTS
 All versions, plus listed versions
0.6-20.7.1-1
 None known
mistune
Ubuntu:18.04:LTS
 All versions, plus listed versions
0.7.4-10.8-10.8.1-10.8.3-2
 None known
mistune
Ubuntu:20.04:LTS
 All versions, plus listed versions
0.8.4-10.8.4-2
 None known
mistune
Ubuntu:22.04:LTS
 All versions, plus listed versions
0.8.4-40.8.4-52.0.0-1+really0.8.4-1
 None known
mistune
Ubuntu:24.04:LTS
 All versions, plus listed versions
2.0.4-23.0.2-1
 None known
mistune
Ubuntu:26.10
 All versions, plus listed versions
3.1.4-1
 None known
mistune
Ubuntu:26.04:LTS
 All versions, plus listed versions
3.1.3-13.1.4-1
 None known
python-mistune
openSUSE:Tumbleweed
From an advisory covering 4 CVEs
 before 3.4.0-2.1
3.4.0-2.1

History

History
RecordedChangedSources
affected, facts
affected, aliases, facts, referencesOSV
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-115348 is a high vulnerability (CVSS 8.7) in Lepture Mistune, published October 22, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.44%, the 38th percentile. No source names a fixed version.

References

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