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CVE-2021-26813

markdown2 Regular Expression Denial of Service

7.5 HighFix available

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

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

2.32%Up 1.8 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 7.5

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
CVE-2021-26813
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:N/I:N/A:P
Weakness
CWE-1333
Updated
2026-11-02
CVE List No score

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
CVE-2021-26813
Updated
2026-11-02
EUVDEUVD-2021-0118 No score

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
EUVD-2021-0118
Updated
2026-11-03
GitHub AdvisoriesGHSA-jr9p-r423-9m2r 8.7

markdown2 Regular Expression Denial of Service

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
GHSA-jr9p-r423-9m2r
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-1333
Updated
2026-11-02
OSV 7.5

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
CVE-2021-26813
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
OSVDEBIAN-CVE-2021-26813 7.5

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
DEBIAN-CVE-2021-26813
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
Show 8 moreShow less
OSVGHSA-jr9p-r423-9m2r 8.7

markdown2 Regular Expression Denial of Service

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
GHSA-jr9p-r423-9m2r
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-1333
Updated
2026-11-02
OSVUBUNTU-CVE-2021-26813 7.5

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
UBUNTU-CVE-2021-26813
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-2021:0429-1 No score

Security update for python-markdown2

This update for python-markdown2 fixes the following issues:

Update to 2.4.0 (boo#1181270):

  • [pull #377] Fixed bug breaking strings elements in metadata lists

  • [pull #380] When rendering fenced code blocks, also add the language-LANG class

  • [pull #387] Regex DoS fixes (CVE-2021-26813, boo#1183171)

  • Switch off failing tests (gh#trentm/python-markdown2#388), ignore failing test suite.

update to 2.3.9:

  • [pull #335] Added header support for wiki tables

  • [pull #336] Reset _toc when convert is run

  • [pull #353] XSS fix

  • [pull #350] XSS fix

  • Add patch to fix unsanitized input for cross-site scripting (boo#1171379)

Record
openSUSE-SU-2021:0429-1
Updated
2026-11-02
OSVopenSUSE-SU-2021:0451-1 No score

Security update for python-markdown2

This update for python-markdown2 fixes the following issues:

Update to 2.4.0 (boo#1181270):

  • [pull #377] Fixed bug breaking strings elements in metadata lists

  • [pull #380] When rendering fenced code blocks, also add the language-LANG class

  • [pull #387] Regex DoS fixes (CVE-2021-26813, boo#1183171)

  • Switch off failing tests (gh#trentm/python-markdown2#388), ignore failing test suite.

update to 2.3.9:

  • [pull #335] Added header support for wiki tables

  • [pull #336] Reset _toc when convert is run

  • [pull #353] XSS fix

  • [pull #350] XSS fix

  • Add patch to fix unsanitized input for cross-site scripting (boo#1171379)

This update was imported from the openSUSE:Leap:15.2:Update update project.

Record
openSUSE-SU-2021:0451-1
Updated
2026-11-02
OSVopenSUSE-SU-2024:11237-1 No score

python36-markdown2-2.4.0-2.4 on GA media

These are all security issues fixed in the python36-markdown2-2.4.0-2.4 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:11237-1
Updated
2026-11-02
OSVopenSUSE-SU-2024:14146-1 No score

python310-markdown2-2.4.13-1.2 on GA media

These are all security issues fixed in the python310-markdown2-2.4.13-1.2 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:14146-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:12016-1 No score

python313-markdown2-2.5.5-1.3 on GA media

These are all security issues fixed in the python313-markdown2-2.5.5-1.3 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:12016-1
Updated
2026-11-02
OSVPYSEC-2021-20 No score

markdown2 >=1.0.1.18, fixed in 2.4.0, is affected by a regular expression denial of service vulnerability. If an attacker provides a malicious string, it can make markdown2 processing difficult or delayed for an extended period of time.

Record
PYSEC-2021-20
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
markdown2
PyPI
 1.0.1.18 up to 2.4.0
2.4.0
python-markdown2
Debian:12
 before 2.3.10-1.1
2.3.10-1.1
python-markdown2
Debian:13
 before 2.3.10-1.1
2.3.10-1.1
python-markdown2
Debian:14
 before 2.3.10-1.1
2.3.10-1.1
markdown2
PyPI
 1.0.1.18 up to 2.4.0, plus listed versions
1.0.1.191.1.01.1.11.2.01.3.0
Show 22 moreShow less
1.3.11.4.01.4.11.4.22.0.02.0.12.1.02.2.02.2.12.2.22.2.32.3.02.3.12.3.102.3.22.3.32.3.42.3.52.3.62.3.72.3.82.3.9
2.4.0
markdown2
PyPI
 1.0.1.18 up to 2.4.0, plus listed versions
1.0.1.191.1.01.1.11.2.01.3.0
Show 22 moreShow less
1.3.11.4.01.4.11.4.22.0.02.0.12.1.02.2.02.2.12.2.22.2.32.3.02.3.12.3.22.3.32.3.42.3.52.3.62.3.72.3.82.3.92.3.10
2.4.0
python-markdown2
Ubuntu:20.04:LTS
 All versions, plus listed versions
2.3.7-2
 None known
python-markdown2
Ubuntu:22.04:LTS
 All versions, plus listed versions
2.3.10-1.12.4.1-1
 None known
python-markdown2
Ubuntu:24.04:LTS
 All versions, plus listed versions
2.4.1-12.4.11-1
 None known
python-markdown2
Ubuntu:25.10
 All versions, plus listed versions
2.4.11-1
 None known
Show 7 moreShow less
Affected packages
PackageAffectedFixed
python-markdown2
Ubuntu:26.10
 All versions, plus listed versions
2.5.4-3
 None known
python-markdown2
Ubuntu:26.04:LTS
 All versions, plus listed versions
2.4.11-12.5.4-22.5.4-3
 None known
python-markdown2
openSUSE:Leap 15.2
 before 2.4.0-lp152.2.3.1
2.4.0-lp152.2.3.1
python-markdown2
SUSE:Package Hub 15 SP2
 before 2.4.0-bp152.2.4.1
2.4.0-bp152.2.4.1
python-markdown2
openSUSE:Tumbleweed
From an advisory covering 2 CVEs
 before 2.4.0-2.4
2.4.0-2.4
python-markdown2
openSUSE:Tumbleweed
From an advisory covering 2 CVEs
 before 2.4.13-1.2
2.4.13-1.2
python-markdown2
openSUSE:Tumbleweed
From an advisory covering 2 CVEs
 before 2.5.5-1.3
2.5.5-1.3

History

History
RecordedChangedSources
affected, facts
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

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

In short

CVE-2021-26813 is a high vulnerability (CVSS 7.5) in Markdown2 Project Markdown2, published March 3, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 2.32%, the 83rd percentile. Fixed in markdown2 2.4.0.

References

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