CVE Intelligence
High Denial of service exploit reference

CVE-2021-3807 — Inefficient Regular Expression Complexity in chalk/ansi-regex

ansi-regex is vulnerable to Inefficient Regular Expression Complexity

Published Sep 17, 2021 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: @huntrdev

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 3.6% (30-day exploitation probability)+13
  • Technical severity (high)+6
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
3.55%
ahead of 89% of scored CVEs · Oct 14, 2026
Affects
Ansi-regex Project
Ansi-regex and 2 more
CVSS base
7.5
High · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — github.com (NIST National Vulnerability Database)
  • Documented patch — huntr.dev (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Ansi-regex Project Ansi-regex, Chalk Chalk/ansi-regex, Oracle Communications Cloud Native Core Policy).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. Search available logs for exploit probes matching the vulnerability class (denial of service), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Ansi-regex Project Ansi-regex ≥ 4.0.0 and < 4.1.1version 3.0.0version 5.0.0version 6.0.0 Vulnerable NIST National Vulnerability Database
Chalk Chalk/ansi-regex < 6.0.1< 5.0.1 Vulnerable CVE Program (cve.org) e CISA ADP
Oracle Communications Cloud Native Core Policy version 1.15.0 Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
7.5 CVSS 3.1 High 3.9 3.6 nvd@nist.gov via NIST National Vulnerability Database
7.5 CVSS 3.0 High 3.9 3.6 security@huntr.dev via NIST National Vulnerability Database
7.5 CVSS 3.0 High — — @huntrdev via CVE Program (cve.org) e CISA ADP
7.8 CVSS 2.0 High 10.0 6.9 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-1333 · Inefficient Regular Expression Complexity (ReDoS)

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 3.55%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Track CPU/memory spikes and availability drops correlated with request patterns.
web/proxy/WAF logsnetwork IDS/IPSresource metrics

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · chalk/chalk/ansi-regex
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 7.5
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • 2021
  • CVE published
    Sep 17, 2021 · @huntrdev

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

Elsewhere on this site

Ansi-regex Project
every CVE for this vendor
Denial of service
same class
CWE-1333
other pages naming this weakness

Related CVEs (same products)

  • CVE-2022-22963 VMware Tanzu Spring Cloud Function Remote Code Execution Vulnerability KEV Apr 1, 2022
  • CVE-2022-22965 Spring Framework JDK 9+ Remote Code Execution Vulnerability KEV Apr 1, 2022
  • CVE-2021-3737 A flaw was found in python. An improperly handled HTTP response in the HTTP client code of python... Mar 4, 2022
  • CVE-2021-34141 Incorrect Comparison in NumPy Dec 17, 2021
  • CVE-2021-43797 HTTP fails to validate against control chars in header names which may lead to HTTP request smuggling Dec 9, 2021
  • CVE-2021-3572 Improper Input Validation in pip Nov 10, 2021

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-3807 is "Inefficient Regular Expression Complexity in chalk/ansi-regex", rated High. It affects Ansi-regex (Ansi-regex Project); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.5 describes technical severity. EPSS 3.55% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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