CVE-2021-40511: OBDA systems’ Mastro 1.0 is vulnerable to XML Entity Expansion (aka “billion laughs”) attack allowing denial o

This month

HIGH 7.5REMOTEDOWNGRADE

CVE-2021-40511 is a high-severity flaw (CVSS 7.5) affecting mastro. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

OBDA systems’ Mastro 1.0 is vulnerable to XML Entity Expansion (aka “billion laughs”) attack allowing denial of service.

Why this priority

High severity
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	0.9% (top 39%)
CISA exploited list	No
Weakness	CWE-776
Published	2022-06-21
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: obdasystems

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

Am I affected?

Timeline

2022-06-21 17:15 UTCPublished CVE record published
2026-06-17 04:07 UTCUpdated Record last modified

obdasystems mastro DOWNGRADE

Affected: 1.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.0 (Debian / Ubuntu)

apt-cache madison mastro sudo apt install mastro=<VERSION_BEFORE_1.0> sudo apt-mark hold mastro

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

dnf --showduplicates list mastro sudo dnf downgrade mastro-<VERSION_BEFORE_1.0> sudo dnf versionlock add mastro

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-2021-40511?

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

Is CVE-2021-40511 being exploited?

CVE-2021-40511 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-2021-40511 affect?

CVE-2021-40511 affects mastro. Severity is high (CVSS 7.5). OBDA systems’ Mastro 1.0 is vulnerable to XML Entity Expansion (aka “billion laughs”) attack allowing denial of service.

How urgent is CVE-2021-40511?

Priority 47/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2021-40510 HIGH 7.5 DOWNGRADE XML eXternal Entity (XXE) in OBDA systems’ Mastro 1.0 allows remote attackers to read system files via custom

References

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