VulnerabilityPublished 29 Sep 2026Updated 8 Nov 2026

CVE-2026-76875: PyPy · Use After Free

Affects PyPySource CVE Database V5

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Not known to be exploited · CVSS 6.3 Medium : upgrade to 3.12.14 or 3.11.16 when convenient.

Data as of 8 Nov 2026, 14:32 UTC

CVSS 4.0 base score

6.3Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (VulnCheck)	CVSS 4.0	6.3
CNA (VulnCheck)	CVSS 3.1	5.3

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers can reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-02.

Patch

Available – fixed in 3.12.14, 3.11.16

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
Vulnerable system availability: None
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: 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: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
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: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within 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 29 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 8 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 PyPy to 3.12.14 or 3.11.16.

Affected software

Product	Affected	Fixed in
PyPyPyPy	Affected >=3.12.0 <3.12.14	Fixed in 3.12.14
PyPyPyPy	Affected <3.11.16	Fixed in 3.11.16
GitHubPyPy`pkg:github/PyPy`Other threats	Affected <3.11.16 >=3.12.0 <3.12.14	Fixed in 3.11.16 3.12.14

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

AI-suggested

Upgrade PyPy to version 3.11.16 or later, or 3.12.14 or later, where this vulnerability is fixed. No other mitigation is indicated or required.

Description

CVE-2026-76875 is a use-after-free vulnerability in PyPy's pyexpat module affecting versions before 3.11.16 and 3.12.14. It occurs when an application creates external-entity sub-parsers without retaining a reference to the parent parser, allowing memory corruption via crafted XML documents.

Impact

An attacker can cause memory corruption by supplying a crafted XML document to vulnerable PyPy applications that create external-entity sub-parsers without retaining the parent parser reference. This can potentially lead to application instability or crashes. The CVSS 4.0 score is 6.3, indicating a medium severity impact with network attack vector and low complexity.

Summary

PyPy versions prior to 3.11.16 and 3.12.14 contain a use-after-free vulnerability in the pyexpat module's ExternalEntityParserCreate function. The vulnerability arises because the child parser retains a raw C back-pointer to the parent parser struct, but PyPy's tracing garbage collector can free the parent's C struct if the parent reference is not retained. This leads to dereferencing a freed pointer during XML parsing, causing memory corruption.

References

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