VulnerabilityPublished 13 Aug 2026Updated 17 Sep 2026

CVE-2026-12075: Gptline · Natural Language Toolkit (NLTK): DNS-rebinding SSRF filter bypass in nltk.pathsec.urlopen (nltk.download / nltk.data.load) defeats ENFORCE mode

Affects gptlineSource GCVE Database

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Not known to be exploited · CVSS 8.6 High : upgrade to 1.0.8_22 soon.

Data as of 18 Sep 2026, 02:18 UTC

CVSS 3.1 base score

8.6High

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

Patch: Available – fixed in 3.10.0, 1.0.8_22

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: None
Availability: None

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 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 30 Oct 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_22; nltk to 3.10.0.

Affected software

Product	Affected	Fixed in
PyPInltk	Affected <3.10.0	Fixed in 3.10.0
Homebrewgptline`pkg:brew/gptline`Other threats	Affected >=1.0.8 <1.0.8_22	Fixed in 1.0.8_22

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 to fix this vulnerability. Users should apply the official update from the NLTK maintainers to ensure the SSRF filter properly prevents DNS rebinding attacks. Until patched, relying on the ENFORCE mode alone is insufficient to block SSRF via DNS rebinding. No vendor advisory text contradicts this; therefore, upgrading to the fixed version is the recommended mitigation.

Description

NLTK's pathsec module includes an SSRF filter intended to block access to loopback, private, link-local, and multicast IP ranges. However, this filter can be bypassed via DNS rebinding, where the hostname resolves to a public IP during validation but resolves to an internal or loopback IP at connection time. This bypass defeats the strict ENFORCE mode, allowing unauthorized access to internal services. The vulnerability is identified as CVE-2026-12075 and has a high severity score of 8.6. A patch is available to address this issue.

Impact

This vulnerability allows an attacker to bypass NLTK's SSRF protections and access internal or loopback network resources that should be restricted. The impact includes unauthorized disclosure of sensitive internal data or services that are normally inaccessible from external sources. The CVSS score of 8.6 reflects a high severity due to network attack vector, low complexity, no privileges required, no user interaction, and high confidentiality impact. There is no indication of integrity or availability impact.

Summary

The vulnerability in NLTK's pathsec.urlopen function arises because hostname resolution occurs twice independently: once during validation via validate_network_url() and again during the actual HTTP connection by urllib. The validation step resolves the hostname and checks the IP against restricted ranges, but the connection step re-resolves the hostname without consulting the validation cache. An attacker controlling DNS can exploit this by returning a public IP for the validation lookup and a loopback or private IP for the connection lookup, bypassing the SSRF filter even under ENFORCE mode. The lru_cache on the validation resolver does not protect the connection resolver, resulting in a false sense of security. Proof-of-concept code demonstrates accessing a loopback-only internal service using this DNS rebinding technique.

CWE-918Server-Side Request Forgery (opens in a new tab)
Base weaknessCWE Top 25 (2025): #22OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
Implementation · Operation
If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
Implementation · Operation
If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
OWASP Cheat Sheets
Server Side Request Forgery Prevention (opens in a new tab)
Unvalidated Redirects and Forwards (opens in a new tab)
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.6.1 (opens in a new tab)
V5.2.6 (opens in a new tab)
Attack patterns
Server Side Request Forgery (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Affected software

Description

AI analysisMachine-generated, updated 18 Sep 2026, 02:18 UTC

WeaknessesCWE-918

Technical details

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