CVE-2021-33570: Postbird 0.8.4 allows stored XSS via the onerror attribute of an IMG element in any PostgreSQL database table

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MEDIUM 5.4DOWNGRADE

CVE-2021-33570 is a medium-severity flaw (CVSS 5.4) affecting postbird. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Postbird 0.8.4 allows stored XSS via the onerror attribute of an IMG element in any PostgreSQL database table. This can result in reading local files via vectors involving XMLHttpRequest and open of a file:/// URL, or discovering PostgreSQL passwords via vectors involving Window.localStorage and savedConnections.

Why this priority

Public exploit reference

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

Risk facts

CVSS score	5.4 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	Required
EPSS exploit chance	3.6% (top 11%)
CISA exploited list	No
Weakness	CWE-79
Published	2021-05-25
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: postbird project

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

Am I affected?

Timeline

2021-05-25 22:15 UTCPublished CVE record published
2026-06-17 03:54 UTCUpdated Record last modified

postbird project postbird DOWNGRADE

Affected: 0.8.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 0.8.4

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 0.8.4 (Debian / Ubuntu)

apt-cache madison postbird sudo apt install postbird=<VERSION_BEFORE_0.8.4> sudo apt-mark hold postbird

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

dnf --showduplicates list postbird sudo dnf downgrade postbird-<VERSION_BEFORE_0.8.4> sudo dnf versionlock add postbird

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.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Exploit-DB: Postbird 0.8.4 - Javascript Injection

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-2021-33570?

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

Is CVE-2021-33570 being exploited?

CVE-2021-33570 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-2021-33570 affect?

CVE-2021-33570 affects postbird. Severity is medium (CVSS 5.4). Postbird 0.8.4 allows stored XSS via the onerror attribute of an IMG element in any PostgreSQL database table. This can result in reading local files via vectors involving XMLHttpRequest and open of a file:/// URL, or discovering PostgreSQL

How urgent is CVE-2021-33570?

Priority 46/100. Public exploit reference

Software pages

PostgreSQL vulnerabilities

References

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