CVE-2020-26547: Monal before 4.9 does not implement proper sender verification on MAM and Message Carbon (XEP-0280) results

Q: How do I fix CVE-2020-26547?

monal: upgrade to 4.9. Exact commands for each OS are on this page.

Q: Is CVE-2020-26547 being exploited?

CVE-2020-26547 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-26547 affect?

CVE-2020-26547 affects monal. Severity is critical (CVSS 9.8). Monal before 4.9 does not implement proper sender verification on MAM and Message Carbon (XEP-0280) results. This allows a remote attacker (able to send stanzas to a victim) to inject arbitrary messages into the local history, with full con

Q: How urgent is CVE-2020-26547?

Priority 51/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.8REMOTEUPGRADE

CVE-2020-26547 is a critical-severity flaw (CVSS 9.8) affecting monal. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Monal before 4.9 does not implement proper sender verification on MAM and Message Carbon (XEP-0280) results. This allows a remote attacker (able to send stanzas to a victim) to inject arbitrary messages into the local history, with full control over the sender and receiver displayed to the victim.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.6% (top 54%)
CISA exploited list	No
Weakness	CWE-345
Published	2021-02-01
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: monal

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

Am I affected?

Timeline

2021-02-01 02:15 UTCPublished CVE record published
2026-06-17 03:08 UTCUpdated Record last modified

monal monal UPGRADE

Affected: < 4.9

Fixed in: 4.9

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 4.9 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade monal

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade monal

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2020-26547?

monal: upgrade to 4.9. Exact commands for each OS are on this page.

Is CVE-2020-26547 being exploited?

CVE-2020-26547 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-2020-26547 affect?

CVE-2020-26547 affects monal. Severity is critical (CVSS 9.8). Monal before 4.9 does not implement proper sender verification on MAM and Message Carbon (XEP-0280) results. This allows a remote attacker (able to send stanzas to a victim) to inject arbitrary messages into the local history, with full con

How urgent is CVE-2020-26547?

Priority 51/100. Critical severity; Remotely exploitable, no login, no user action

References

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