CVE-2020-26148: md_push_block_bytes in md4c.c in md4c 0.4.5 allows attackers to trigger use of uninitialized memory, and cause

This week

HIGH 7.5REMOTEDOWNGRADE

CVE-2020-26148 is a high-severity flaw (CVSS 7.5) affecting md4c. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

md_push_block_bytes in md4c.c in md4c 0.4.5 allows attackers to trigger use of uninitialized memory, and cause a denial of service (e.g., assertion failure) via a malformed Markdown document.

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.4% (top 27%)
CISA exploited list	No
Weakness	CWE-908
Published	2020-09-30
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: md4c project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-09-30 18:15 UTCPublished CVE record published
2026-06-17 03:07 UTCUpdated Record last modified

md4c project md4c DOWNGRADE

Affected: 0.4.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.4.5

1. Check installed version

apt-cache policy md4c || rpm -q md4c || md4c --version

2. No fixed release: DOWNGRADE to a release before 0.4.5 (Debian / Ubuntu)

apt-cache madison md4c sudo apt install md4c=<VERSION_BEFORE_0.4.5> sudo apt-mark hold md4c

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list md4c sudo dnf downgrade md4c-<VERSION_BEFORE_0.4.5> sudo dnf versionlock add md4c

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-26148?

md4c: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-26148 being exploited?

CVE-2020-26148 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-26148 affect?

CVE-2020-26148 affects md4c. Severity is high (CVSS 7.5). md_push_block_bytes in md4c.c in md4c 0.4.5 allows attackers to trigger use of uninitialized memory, and cause a denial of service (e.g., assertion failure) via a malformed Markdown document.

How urgent is CVE-2020-26148?

Priority 54/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-30027 MEDIUM 5.5 DOWNGRADE md_analyze_line in md4c.c in md4c 0.4.7 allows attackers to trigger use of uninitialized memory, and cause a d
CVE-2018-12112 HIGH 7.8 DOWNGRADE md_build_attribute in md4c.c in md4c 0.2.6 allows remote attackers to cause a denial of service (Segmentation
CVE-2018-12102 MEDIUM 5.5 DOWNGRADE md4c 0.2.6 has a NULL pointer dereference in the function md_process_line in md4c.c, related to ctx->current_b
CVE-2018-11547 CRITICAL 9.8 DOWNGRADE md_is_link_reference_definition_helper in md4c 0.2.5 has a heap-based buffer over-read because md_is_link_labe
CVE-2018-11546 CRITICAL 9.8 DOWNGRADE md4c 0.2.5 has a heap-based buffer over-read because md_is_named_entity_contents has an off-by-one error.

References

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