An issue was discovered in the stripTags and unescapeHTML components in Prototype 1.7.3 where an attacker can cause a Regular Expression De…

published 2021-06-21 5 y ago modified 2026-06-17 4 mo ago also EUVD-2020-20021

cvss: 7.5; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 3.3%; EPSS 3.3% chance of exploitation in 30 days, percentile 88%
public exploits: 0; none known

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.

Patch / fix

distros 1

prototypejs Debian 14, Debian 13, Debian 12 1.7.3-1

debian advisories DEBIAN-CVE-2020-27511

Exploit prediction

3.34% chance of exploitation in the next 30 days, higher than 88% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/prototypejs/prototype/blob/dee2f7d8611248abce81287e1be4156011953c90/src/prototype/lang/string.js#L283 referenced PoC, tagged "exploit" by a source, unverified
github.com https://github.com/yetingli/PoCs/blob/main/CVE-2020-27511/Prototype.md referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD	2.0	5.0	AV:N/AC:L/Au:N/C:N/I:N/A:P

References

github.com /prototypejs/prototype/blob/dee2f7d8611248abce81287e1be4156011953c90/src/prototype/lang/string.js#L283
exploit, third-party-advisory
github.com /yetingli/PoCs/blob/main/CVE-2020-27511/Prototype.md
exploit, third-party-advisory
prototypejs.org /
vendor-advisory

Sources

CVE List CVE-2020-27511
NVD CVE-2020-27511

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary