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CVE-2020-5238

Denial of service in table parsing in cmark-gfm

6.5 MediumFix available

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
Low
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

1.57%Unchanged since Apr 14, 2021
90%50%10%1%

What each source reports

CVE List Score used 6.5

Denial of service in table parsing in cmark-gfm

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Record
CVE-2020-5238
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-20
Updated
2026-11-02
EUVDEUVD-2020-26457 6.5

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Record
EUVD-2020-26457
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-03
NVD 6.5

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Record
CVE-2020-5238
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CVSS 2.0
4.0 MediumAV:N/AC:L/Au:S/C:N/I:N/A:P
Weakness
CWE-20
Updated
2026-11-02
OSV 6.5

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Record
CVE-2020-5238
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2020-5238 6.5

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Record
DEBIAN-CVE-2020-5238
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVRHSA-2021:1972 6.5

Red Hat Security Advisory: pandoc security update

Record
RHSA-2021:1972
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2020-5238 6.5

The table extension in GitHub Flavored Markdown before version 0.29.0.gfm.1 takes O(n * n) time to parse certain inputs. An attacker could craft a markdown table which would take an unreasonably long time to process, causing a denial of service. This issue does not affect the upstream cmark project. The issue has been fixed in version 0.29.0.gfm.1.

Record
UBUNTU-CVE-2020-5238
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVALSA-2021:1972 No score

Moderate: pandoc security update

Pandoc is a Haskell library for converting from one markup format to another, and a command-line tool that uses this library.

Security Fix(es):

  • cmark-gfm: Exponential time to parse certain inputs could lead to DoS (CVE-2020-5238)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Additional Changes:

For detailed information on changes in this release, see the AlmaLinux Release Notes linked from the References section.

Record
ALSA-2021:1972
Updated
2026-11-02
OSVRSEC-2023-6 No score

Denial of Service (DoS) vulnerability

The commonmark package, specifically in its dependency on GitHub Flavored Markdown before version 0.29.0.gfm.1, has a vulnerability related to time complexity. Parsing certain crafted markdown tables can take O(n * n) time, leading to potential Denial of Service attacks. This issue does not affect the upstream cmark project and has been fixed in version 0.29.0.gfm.1.

Record
RSEC-2023-6
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
pandoc
AlmaLinux:8
 before 2.0.6-5.el8
2.0.6-5.el8
pandoc-common
AlmaLinux:8
 before 2.0.6-5.el8
2.0.6-5.el8
cmark-gfm
Debian:12
 before 0.29.0.gfm.2-1
0.29.0.gfm.2-1
cmark-gfm
Debian:13
 before 0.29.0.gfm.2-1
0.29.0.gfm.2-1
cmark-gfm
Debian:14
 before 0.29.0.gfm.2-1
0.29.0.gfm.2-1
haskell-cmark-gfm
Debian:12
 before 0.2.1+ds1-1
0.2.1+ds1-1
haskell-cmark-gfm
Debian:13
 before 0.2.1+ds1-1
0.2.1+ds1-1
haskell-cmark-gfm
Debian:14
 before 0.2.1+ds1-1
0.2.1+ds1-1
python-cmarkgfm
Debian:12
 before 0.7.0-1
0.7.0-1
python-cmarkgfm
Debian:13
 before 0.7.0-1
0.7.0-1
Show 30 moreShow less
Affected packages
PackageAffectedFixed
python-cmarkgfm
Debian:14
 before 0.7.0-1
0.7.0-1
r-cran-commonmark
Debian:12
 before 1.8.0-1
1.8.0-1
r-cran-commonmark
Debian:13
 before 1.8.0-1
1.8.0-1
r-cran-commonmark
Debian:14
 before 1.8.0-1
1.8.0-1
ruby-commonmarker
Debian:12
 before 0.21.0-1
0.21.0-1
ruby-commonmarker
Debian:13
 before 0.21.0-1
0.21.0-1
ruby-commonmarker
Debian:14
 before 0.21.0-1
0.21.0-1
pandoc
Red Hat:enterprise_linux:8::crb
 before 0:2.0.6-5.el8
0:2.0.6-5.el8
pandoc-common
Red Hat:enterprise_linux:8::crb
 before 0:2.0.6-5.el8
0:2.0.6-5.el8
commonmark
CRAN
 0.2 up to 1.8, plus listed versions
0.40.50.60.70.8
Show 8 moreShow less
0.91.01.11.21.41.51.61.7
1.8
cmark-gfm
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
0.28.3.gfm.20-30.29.0.gfm.0-30.29.0.gfm.0-40.29.0.gfm.0-4ubuntu0.1~esm1
 None known
haskell-cmark-gfm
Ubuntu:20.04:LTS
 All versions, plus listed versions
0.1.8-1build1
 None known
python-cmarkgfm
Ubuntu:20.04:LTS
 All versions, plus listed versions
0.4.2-1build10.4.2-1build2
 None known
r-cran-commonmark
Ubuntu:20.04:LTS
 All versions, plus listed versions
1.7-1
 None known
ruby-commonmarker
Ubuntu:20.04:LTS
 All versions, plus listed versions
0.17.9-10.20.2-1build1
 None known
haskell-cmark-gfm
Ubuntu:22.04:LTS
 All versions, plus listed versions
0.2.1+ds1-1build10.2.1+ds1-2build10.2.1+ds1-2build2
 None known
python-cmarkgfm
Ubuntu:22.04:LTS
 All versions, plus listed versions
0.4.2-1build30.4.2-1build50.8.0-1
 None known
r-cran-commonmark
Ubuntu:22.04:LTS
 All versions, plus listed versions
1.7-2
 None known
haskell-cmark-gfm
Ubuntu:24.04:LTS
 All versions, plus listed versions
0.2.5+ds1-1build20.2.5+ds1-2
 None known
python-cmarkgfm
Ubuntu:24.04:LTS
 All versions, plus listed versions
0.8.0-3
 None known
r-cran-commonmark
Ubuntu:24.04:LTS
 All versions, plus listed versions
1.9.0-11.9.1-1
 None known
haskell-cmark-gfm
Ubuntu:25.10
 All versions, plus listed versions
0.2.6+ds1-1
 None known
python-cmarkgfm
Ubuntu:25.10
 All versions, plus listed versions
0.8.0-32024.11.20-1
 None known
r-cran-commonmark
Ubuntu:25.10
 All versions, plus listed versions
1.9.5-1
 None known
haskell-cmark-gfm
Ubuntu:26.10
 All versions, plus listed versions
0.2.6+ds1-3
 None known
python-cmarkgfm
Ubuntu:26.10
 All versions, plus listed versions
2025.10.22-2
 None known
r-cran-commonmark
Ubuntu:26.10
 All versions, plus listed versions
2.0.0-22.0.0-3
 None known
haskell-cmark-gfm
Ubuntu:26.04:LTS
 All versions, plus listed versions
0.2.6+ds1-10.2.6+ds1-3
 None known
python-cmarkgfm
Ubuntu:26.04:LTS
 All versions, plus listed versions
2024.11.20-12025.10.22-12025.10.22-2
 None known
r-cran-commonmark
Ubuntu:26.04:LTS
 All versions, plus listed versions
1.9.5-12.0.0-12.0.0-2
 None known

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, NVD, OSV

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

In short

CVE-2020-5238 is a medium vulnerability (CVSS 6.5) in Github Cmark-gfm, published July 1, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.57%, the 75th percentile. Fixed in pandoc 2.0.6-5.el8.

References

Show 13 moreShow less
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