CVE-2020-27511: An issue was discovered in the stripTags and unescapeHTML components in Prototype 1.7.3 where an attacker can

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HIGH 7.5REMOTEDOWNGRADE

CVE-2020-27511 is a high-severity flaw (CVSS 7.5) affecting prototype. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in the stripTags and unescapeHTML components in Prototype 1.7.3 where an attacker can cause a Regular Expression Denial of Service (ReDOS) through stripping crafted HTML tags.

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	3.3% (top 11%)
CISA exploited list	No
Published	2021-06-21
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: prototypejs

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

Am I affected?

Timeline

2021-06-21 20:15 UTCPublished CVE record published
2026-06-17 03:09 UTCUpdated Record last modified

prototypejs prototype DOWNGRADE

Affected: 1.7.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.7.3

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 1.7.3 (Debian / Ubuntu)

apt-cache madison prototype sudo apt install prototype=<VERSION_BEFORE_1.7.3> sudo apt-mark hold prototype

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

dnf --showduplicates list prototype sudo dnf downgrade prototype-<VERSION_BEFORE_1.7.3> sudo dnf versionlock add prototype

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-2020-27511?

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

Is CVE-2020-27511 being exploited?

CVE-2020-27511 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-2020-27511 affect?

CVE-2020-27511 affects prototype. Severity is high (CVSS 7.5). An issue was discovered in the stripTags and unescapeHTML components in Prototype 1.7.3 where an attacker can cause a Regular Expression Denial of Service (ReDOS) through stripping crafted HTML tags.

How urgent is CVE-2020-27511?

Priority 58/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2020-7993 MEDIUM 4.3 DOWNGRADE Prototype 1.6.0.1 allows remote authenticated users to forge ticket creation (on behalf of other user accounts

References

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