CVE-2026-78681: NLTK versions before 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity de

Q: How do I fix CVE-2026-78681?

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

Q: Is CVE-2026-78681 being exploited?

CVE-2026-78681 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-2026-78681 affect?

CVE-2026-78681 affects nltk. Severity is high (CVSS 7.5). NLTK versions before 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity declarations in document DTDs. Attackers can craft XML payloads with nested entity declarations that expand from hundreds of bytes t

Q: How urgent is CVE-2026-78681?

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

This week

HIGH 7.5REMOTEUPGRADE

CVE-2026-78681 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 versions before 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity declarations in document DTDs. Attackers can craft XML payloads with nested entity declarations that expand from hundreds of bytes to megabytes in memory, causing denial of service.

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-776
Published	2026-08-25
Last modified	2026-10-12

Publisher (CNA): VulnCheck · Vendor: nltk

Last updated 2026-10-12 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-25 02:16 UTCPublished CVE record published
2026-10-12 21:10 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-2026-78681?

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

Is CVE-2026-78681 being exploited?

CVE-2026-78681 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-2026-78681 affect?

CVE-2026-78681 affects nltk. Severity is high (CVSS 7.5). NLTK versions before 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity declarations in document DTDs. Attackers can craft XML payloads with nested entity declarations that expand from hundreds of bytes t

How urgent is CVE-2026-78681?

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

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References

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