CVE-2026-81722: nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity deni

Q: How do I fix CVE-2026-81722?

nltk: upgrade to 3.10.3. Exact commands for each OS are on this page.

Q: Is CVE-2026-81722 being exploited?

CVE-2026-81722 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-81722 affect?

CVE-2026-81722 affects nltk. Severity is high (CVSS 7.5). nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing 'y' characters on

Q: How urgent is CVE-2026-81722?

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

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-81722 is a high-severity flaw (CVSS 7.5) affecting nltk. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing 'y' characters on every call, and _measure() invokes it for each stem position, causing O(n^2) behavior. A single ~20-50 KB untrusted token consisting of a long run of the letter 'y' followed by a matching suffix (e.g., 'ness')

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 56%)
CISA exploited list	No
Weakness	CWE-407
Published	2026-08-27
Last modified	2026-08-31

Publisher (CNA): VulnCheck · Vendor: nltk

Last updated 2026-08-31 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-27 17:21 UTCPublished CVE record published
2026-08-31 15:44 UTCUpdated Record last modified

nltk nltk UPGRADE

Affected: < 3.10.3

Fixed in: 3.10.3

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 3.10.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nltk

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nltk

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2026-81722?

nltk: upgrade to 3.10.3. Exact commands for each OS are on this page.

Is CVE-2026-81722 being exploited?

CVE-2026-81722 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-2026-81722 affect?

CVE-2026-81722 affects nltk. Severity is high (CVSS 7.5). nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing 'y' characters on

How urgent is CVE-2026-81722?

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

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References

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