VulnerabilityPublished 11 Sep 2026Updated 14 Sep 2026

CVE-2026-67211: Apache OpenNLP · Excessive Memory Allocation

Affects Apache OpenNLPSource CVE Database V5

Not known to be exploited · CVSS 7.5 High : upgrade to 3.0.0-M6 soon.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.7% chance of exploitation in 30 days – higher than 54% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 3.0.0-M6

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

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

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: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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.

ghsa-gr8h-7qg5-vh27

What to do

Upgrade Apache to 3.0.0-M6.

Affected software

Product	Affected	Fixed in
Apache Software FoundationApache OpenNLP	Affected >=3.0.0-M4 <3.0.0-M6	Fixed in 3.0.0-M6
MavenApache Software Foundation/org.apache.opennlp:opennlp-symspell`pkg:maven/Apache Software Foundation/org.apache.opennlp:opennlp-symspell`Other threats	Affected >=3.0.0-M4 <3.0.0-M6	Fixed in 3.0.0-M6

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

AI-suggested

A fixed version, Apache OpenNLP 3.0.0-M6, is available and users are strongly advised to upgrade. The fix enforces an upper bound on the size fields in SymSpell model files to prevent excessive memory allocation. Users who cannot upgrade immediately should treat all SymSpell .bin model files as untrusted input unless their provenance is verified and avoid loading models from untrusted sources without integrity checks. The OPENNLP_MAX_ENTRIES system property can be used to adjust the upper bound if larger dictionaries are legitimately required.

Description

CVE-2026-67211 is a high-severity denial of service vulnerability in Apache OpenNLP versions 3.0.0-M4 and 3.0.0-M5. It arises from unbounded memory allocation when deserializing SymSpell model files with attacker-controlled size fields, leading to OutOfMemoryError and process crashes. The issue affects the SymSpellModelSerializer.create() method and all code paths that load SymSpell models from untrusted sources. The vulnerability is fixed in version 3.0.0-M6 by enforcing an upper bound on the size fields to prevent excessive memory allocation.

Impact

The vulnerability allows an attacker to cause a denial of service by crashing JVM processes that load maliciously crafted SymSpell model files. There is no impact on confidentiality or integrity, only availability. The attack requires supplying or loading a crafted model file from untrusted or semi-trusted sources. Legitimate model files are unaffected by the fix.

Summary

The vulnerability occurs in Apache OpenNLP's SymSpellModelSerializer.create() method, which reads two 32-bit signed integer count fields (unigramCount and bigramCount) from a binary SymSpell model file and uses these values to pre-size LinkedHashMaps without an upper bound. An attacker can craft a malicious .bin model file with these counts set to very large values (e.g., Integer.MAX_VALUE), causing the JVM to attempt to allocate extremely large backing arrays (4–8 GB), resulting in an OutOfMemoryError and denial of service. This affects all code paths that deserialize SymSpell models, including command-line tools and model loading mechanisms in the opennlp-spellcheck extension introduced in version 3.0.0-M4. The fix, introduced in version 3.0.0-M6, applies an upper bound (default 10,000,000 entries) to these counts, throwing an IOException if exceeded, preventing large allocations. Users can override this limit via the OPENNLP_MAX_ENTRIES system property if needed.

CWE-789Memory Allocation with Excessive Size Value (opens in a new tab)
Variant weakness
The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.
Implementation · Architecture and Design
Perform adequate input validation against any value that influences the amount of memory that is allocated. Define an appropriate strategy for handling requests that exceed the limit, and consider supporting a configuration option so that the administrator can extend the amount of memory to be used if necessary.
Operation
Run your program using system-provided resource limits for memory. This might still cause the program to crash or exit, but the impact to the rest of the system will be minimized.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
OWASP ASVS 4.0.3
V8.1.4 (opens in a new tab)
V13.4.1 (opens in a new tab)
V11.1.4 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Oct 2026, 00:05 UTC

WeaknessesCWE-789

Technical details

References

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