VulnerabilityPublished 28 Oct 2026

CVE-2026-116795: le0pard re2js · Inefficient Algorithmic Complexity

Affects le0pard re2jsSource CVE Database V5

Not known to be exploited · CVSS 7.5 High : upgrade to 2.8.7 soon.

Data as of 28 Oct 2026, 17:42 UTC

CVSS 3.1 base score

7.5High

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

Patch: Available – fixed in 2.8.7

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 28 Oct 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.

What to do

Upgrade le0pard re2js to 2.8.7.

Affected software

Product	Affected	Fixed in
le0pardre2js	Affected >=2.2.0 <2.8.7	Fixed in 2.8.7

AI-suggested

Upgrade re2js to version 2.8.7 or later, where this vulnerability is fixed. No other mitigation is indicated or required.

Description

CVE-2026-116795 is a high-severity vulnerability in the re2js JavaScript regular expression engine, affecting versions from 2.2.0 up to but not including 2.8.7. The issue arises when LOOKBEHINDS are enabled and repeated matching methods such as matcher().find(), matchAll(), split(), or matcher().replaceAll() are used, causing quadratic time complexity in processing. This inefficiency allows crafted input to monopolize a single-threaded worker, resulting in a denial of service. The vulnerability is fixed in version 2.8.7.

Impact

The vulnerability allows an attacker to cause a denial of service by exploiting inefficient algorithmic complexity in re2js when using LOOKBEHINDS with repeated matching. This results in excessive CPU consumption on a single-threaded worker, potentially making the service unresponsive. There is no impact on confidentiality or integrity.

Summary

RE2JS, a JavaScript port of the RE2 regular expression engine, is designed for linear time matching. However, from versions 2.2.0 through 2.8.6, enabling LOOKBEHINDS combined with repeated matching methods leads to quadratic total work due to the way Machine.match restarts lookbehind scanning from offset zero for each start position. Matcher-based APIs request capture slots that prevent early exit optimizations, causing dense matches to repeatedly rescan input. This behavior can be exploited by attacker-controlled input to cause denial of service by monopolizing processing resources. The issue is resolved in version 2.8.7.

CWE-407Inefficient Algorithmic Complexity (opens in a new tab)
Class weaknessLikelihood of exploit: Low
An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-1333Inefficient Regular Expression Complexity (opens in a new tab)
Base weaknessLikelihood of exploit: High
The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
Architecture and Design
Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
System Configuration
Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
Implementation
Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.1 (opens in a new tab)
Attack patterns
Regular Expression Exponential Blowup (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 28 Oct 2026, 17:28 UTC

WeaknessesCWE-407, CWE-1333

Technical details

References

Community reviews

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