VulnerabilityPublished 2 Sep 2026Updated 17 Sep 2026

CVE-2026-81725: NLTK · Pl196xCorpusReader has quadratic ReDoS on malformed TEI blocks

Affects gptlineSource GCVE Database

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Not known to be exploited · CVSS 6.3 Medium : upgrade to 1.0.8_23 when convenient.

Data as of 1 Nov 2026, 22:58 UTC

CVSS 4.0 base score

6.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 30% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.0.8_23

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: High
Attack Requirements: None
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 1 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade gptline to 1.0.8_23.

Affected software

Product	Affected	Fixed in
Homebrewgptline`pkg:brew/gptline`Other threats	Affected >=1.0.8 <1.0.8_23	Fixed in 1.0.8_23

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available but not yet released. The vendor recommends replacing the lazy regex parser with a linear parser or bounded tokenizer and adding regression tests to ensure near-linear parsing time on malformed inputs. If you cannot patch yet, users should avoid processing untrusted or attacker-controlled corpus files with Pl196xCorpusReader to mitigate risk.

Description

The Pl196xCorpusReader component in the gptline product has a Regular Expression Denial of Service (ReDoS) vulnerability (CVE-2026-81725) caused by quadratic CPU growth when parsing malformed TEI blocks with many unmatched opening tags. This affects versions from 1.0.8 up to but not including 1.0.8_23. The vulnerability arises from lazy regex patterns that repeatedly rescan attacker-controlled text, leading to excessive CPU consumption and potential parser thread stalling.

Impact

Attackers can supply malformed TEI corpus files with many unmatched opening tags to cause the Pl196xCorpusReader to consume excessive CPU resources, leading to denial of service by stalling parser threads. This impacts applications that parse attacker-influenced corpus files using public reader APIs such as words() and tagged_words(). There is no indication of data breach or code execution, only resource exhaustion.

Summary

CVE-2026-81725 is a ReDoS vulnerability in the nltk.corpus.reader.pl196x.Pl196xCorpusReader, specifically in the TEICorpusView.read_block method. The issue is due to lazy '.*?' regexes that rescan malformed TEI blocks containing many unmatched opening tags, causing quadratic CPU time growth during parsing operations such as words() and tagged_words(). Both published version 3.9.4 and source version 3.10.0-rc2 demonstrate the issue. The vulnerability allows an attacker supplying malformed corpus files to cause heavy CPU usage and stall parser threads. A patch is not yet available, but remediation involves replacing the regex-based parser with a linear or bounded tokenizer approach.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Sep 2026, 01:50 UTC

Technical details

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