VulnerabilityPublished 26 Oct 2026

CVE-2026-113715: virtualenv · Venv configuration readback can reinterpret path boundaries

Affects toxSource GCVE Database

Authoritative record:CVE-2026-113715· Low 2.0

Not known to be exploited · CVSS 2.0 Low : upgrade to 4.67.0 when convenient.

Data as of 27 Oct 2026, 06:13 UTC

CVSS 4.0 base score

2.0Low

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

Patch: Available – fixed in 4.67.0

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

Attack Vector: Local
Attack Complexity: High
Attack Requirements: Present
Privileges Required: None
User Interaction: Passive
Vulnerable system confidentiality: Low
Vulnerable system integrity: Low
Vulnerable system availability: Low
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: 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: High: The successful attack depends on the evasion or circumvention of security-enhancing techniques in place that would otherwise hinder the attack. These include: Evasion of exploit mitigation techniques, for example, circumvention of address space randomization (ASLR) or data execution prevention (DEP) must be performed for the attack to be successful; Obtaining target-specific secrets. The attacker must gather some target-specific secret before the attack can be successful. A secret is any piece of information that cannot be obtained through any amount of reconnaissance. To obtain the secret the attacker must perform additional attacks or break otherwise secure measures (e.g. knowledge of a secret key may be needed to break a crypto channel). This operation must be performed for each attacked target.
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: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to 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: 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.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 20 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 tox to 4.67.0.

Affected software

Product	Affected	Fixed in
Homebrewtox`pkg:brew/tox`Other threats	Affected >=3.27.0 <4.67.0	Fixed in 4.67.0

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

Description

## Summary The venv creator reads the standard library's generated pyvenv.cfg with splitlines() and merges all resulting keys over virtualenv's configuration. Line-boundary characters from destination data can therefore become configuration structure before output sanitization. Anthropic's OSS Scanner reported this as `ANT-2026-6ZQHJ6VI` in `virtualenv-20261015-005`, received on 15 October 2026. ## Affected area Configuration readback by the stdlib venv creator. ## Attacker-controlled input An untrusted caller must influence the destination pathname passed to the venv creator. That pathname must contain a character that Python treats as a line boundary. The builtin creator follows a different configuration-writing path. ## Affected code The relevant 21.14.8 source is in [venv readback](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/create/via_global_ref/venv.py), [configuration parser](https://github.com/pypa/virtualenv/blob/a795ab116356afde11039cf2763d77e8a06da738/src/virtualenv/create/pyenv_cfg.py). ## Mechanism With `--creator venv`, virtualenv asks the standard library to create an environment, reads its `pyvenv.cfg` with `str.splitlines()`, and merges the parsed keys over virtualenv's chosen settings. CPython writes the destination into a `command =` value without escaping every character that `splitlines()` recognizes as a line boundary. A destination containing U+2028, for example, can therefore supply new `home` and `include-system-site-packages` keys during readback. Virtualenv writes those keys as real configuration lines. The builtin creator does not use this readback path. ## Reproduction and evidence The scanner used one destination value with U+2028 between `home = /attacker/chosen`, `include-system-site-packages = true`, and an absorbing `x =` key. A `python -m venv --without-pip` control kept the value inside its `command` line and reported the base interpreter's `sys._home`. `virtualenv --creator venv --no-seed` on the same value wrote separate injected configuration lines and its interpreter reported `sys._home = /attacker/chosen`. The path did not require a literal newline byte. The control establishes that the extra keys came from virtualenv's readback, not from the standard library's initial file alone. The altered `home` can change which standard-library files the interpreter loads if an attacker also controls that location; `include-system-site-packages = true` weakens environment isolation. Choosing the venv creator is required, either explicitly or through a rare fallback. The report traces the readback to the 20.x rewrite, first released in 20.0.0b1. [PR #3426](https://github.com/pypa/virtualenv/pull/3426) rejects line-boundary characters before creation and rebuilds the final configuration from selected settings. ## Attack sequence ```mermaid sequenceDiagram participant A as Destination supplier participant S as stdlib venv participant V as virtualenv readback participant C as Final pyvenv.cfg participant P as Environment Python A->>S: path contains U+2028 and home = /attacker/chosen S->>C: write path inside command value V->>C: read with splitlines() V->>V: parse suffix as separate keys V->>C: rewrite home and include-system-site-packages P->>C: read injected keys on startup C-->>P: sys._home changes and isolation is disabled ``` ## Reproducer files The following files are from the scanner report for `ANT-2026-6ZQHJ6VI`. They were tested against commit `a857a7823c73` in the scanner image. The `repro` entrypoint expects companion files under `/tmp/repro.d`; cases that change user IDs need a disposable root-capable container. The last output line is `BUG` when the reported behavior occurs. These files are included as evidence and were not rerun for this advisory update. **`repro`** ```text #!/usr/bin/env python3 import os import shutil import subprocess work = "/tmp/repro-venv-creator-cfg" shutil.rmtree(work, ignore_errors=True) # the attacker's input: the text of a destination path. # U+2028 ends a line for str.splitlines() but not for CPython's own pyvenv.cfg reader. # The slashes only make nested directories; the last key, x, absorbs the rest of the path. LS = "\u2028" dest = f"{work}/proj{LS}home = /attacker/chosen{LS}include-system-site-packages = true{LS}x = /env" base_python = os.path.realpath(shutil.which("python")) real_home = os.path.dirname(base_python) def pyvenv_cfg_lines(env): # split on "\n" only, as the interpreter does return open(f"{env}/pyvenv.cfg", encoding="utf-8").read().split("\n") def sys_home(env): # site.py sets sys._home from the `home` key of the environment's pyvenv.cfg probe = [f"{env}/bin/python", "-c", "import sys; print(sys._home)"] return subprocess.run(probe, capture_output=True, text=True, check=True).stdout.strip() # control: the same path through the standard library alone stdlib_env = dest + "-stdlib"

References

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