VulnerabilityPublished 22 Mar 2026Updated 23 Mar 2026

CVE-2026-4539: pygments · ReDoS

Affects pygmentsSource CVE Database V5

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Public exploit available · CVSS 4.8 Medium.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score

4.8Medium

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

EPSS: 0.1% chance of exploitation in 30 days – higher than 5% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Base metrics

Attack Vector: Local
Attack Complexity: Low
Attack Requirements: None
Privileges Required: Low
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

Threat metrics

Exploit Maturity: POC

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

Attack Vector: Local: The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
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: Low: The attacker requires privileges that provide basic capabilities that are typically limited to settings and resources owned by a single low-privileged user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.
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.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
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), CVSS vector, 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

Affected software

Product	Affected	Fixed in
pygments	Affected =2.19.0 =2.19.1 =2.19.2	Fixed in–
PyPIpygments`pkg:pypi/pygments`Other threats	Affected =2.19.0 =2.19.1 =2.19.2	Fixed in–

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

AI-suggested

To mitigate CVE-2026-4539, organizations should first restrict local access to trusted users only, minimizing the risk of exploitation by unprivileged local attackers. Until an official patch is released, consider implementing input validation or sanitization to limit or reject inputs that could trigger complex regular expression processing in the AdlLexer function. Monitoring system resource usage for unusual CPU spikes during pygments execution can help detect exploitation attempts. If feasible, isolate or sandbox processes using pygments to contain potential denial of service impacts. Organizations may also evaluate alternative syntax highlighting libraries without this vulnerability or downgrade to earlier unaffected versions if applicable. Engage with the pygments project or community to track patch releases and apply updates promptly once available. Additionally, review internal policies on local user permissions and code execution rights to reduce exposure. Finally, educate developers and system administrators about the risk of ReDoS vulnerabilities and the importance of cautious handling of untrusted input in code analysis tools.

Description

CVE-2026-4539 is a medium severity vulnerability in the pygments library versions 2.19.0 through 2.19.2, specifically in the AdlLexer function within pygments/lexers/archetype.py. The flaw arises from inefficient regular expression complexity, which can be exploited locally by an attacker with limited privileges to cause performance degradation or denial of service. No user interaction or authentication beyond local access is required, and no integrity or confidentiality impact is reported. The vulnerability has a CVSS score of 4.8, reflecting its moderate risk.

Impact

The primary impact of CVE-2026-4539 is on system availability. An attacker with local access and limited privileges can exploit inefficient regular expression processing to cause high CPU usage, potentially leading to denial of service conditions. This can disrupt applications or services that rely on pygments for syntax highlighting or code analysis, especially if they process untrusted or user-supplied input. While the vulnerability does not compromise confidentiality or integrity, the resulting service degradation can affect developer productivity, automated tooling, or any systems embedding pygments. Organizations with multi-user environments or shared systems where local users have access to run code or commands involving pygments are at higher risk. The lack of a patch and the public availability of exploit code increase the likelihood of exploitation in such environments. However, the requirement for local access limits the threat to internal or compromised hosts rather than remote attackers. Overall, the impact is moderate but could be significant in environments where availability is critical and local user access is common.

References

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