VulnerabilityPublished 10 Nov 2026

CVE-2026-123370: compose-lint · `fix --apply` can delete a line the user did not select, including a security setting

Affects compose-lintSource GCVE Database

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Authoritative record:CVE-2026-123370· Medium 5.1

Not known to be exploited · CVSS 5.1 Medium : upgrade to 0.18.0 when convenient.

Data as of 10 Nov 2026, 17:47 UTC

CVSS 4.0 base score

5.1Medium

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

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 4.0	5.1

Patch: Available – fixed in 0.18.0

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

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: Active
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: Low
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: 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: 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: Active: Successful exploitation of this vulnerability requires a targeted user to perform specific, conscious interactions with the vulnerable system and the attacker’s payload, or the user’s interactions would actively subvert protection mechanisms which would lead to exploitation of the vulnerability.
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: 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 Subsequent 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 9 Nov 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 10 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 compose-lint to 0.18.0.

Affected software

Product	Affected	Fixed in
PyPIcompose-lint	Affected >=0.9.0 <0.18.0	Fixed in 0.18.0

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

AI-suggested

Upgrade compose-lint to version 0.18.0 or later, where the issue is fixed. If using older versions, carefully review the dry-run diff output before applying fixes with `fix --apply`, and avoid running `fix --apply` on files from untrusted sources. The GitHub Action does not run `fix` and is not affected.

Description

A flaw in compose-lint versions 0.9.0 through 0.17.0 causes the `fix --apply` command to incorrectly delete lines following the intended fix line when certain Unicode line break characters are present inside quoted values. This can unintentionally remove security-related settings such as network restrictions. The issue arises from inconsistent line break handling between the YAML parser and the fix application logic. The problem is fixed in version 0.18.0, which unifies line break definitions and rejects files with ambiguous line breaks.

Impact

The vulnerability can cause `compose-lint fix --apply` to delete unintended lines in Compose files, including security settings such as internal network restrictions. This silent removal can weaken container isolation and security posture without detection, as the tool reports successful fixes and subsequent checks pass. The issue affects local usage of the compose-lint Docker image versions 0.9.0 through 0.17.0. The GitHub Action is not affected. There is no evidence of exploitation in the wild.

Summary

The vulnerability in compose-lint (CVE-2026-123370) affects versions 0.9.0 through 0.17.0 when running `fix --apply`. The tool converts line numbers to file positions assuming only LF (`\n`) as line breaks, but the YAML parser also treats lone carriage return, U+0085, U+2028, and U+2029 as line breaks. This mismatch causes edits to shift by one line, leading to deletion of lines following the intended fix. For example, fixing a logging configuration line inadvertently removes the subsequent network configuration line, potentially weakening security by moving services off internal networks. The command reports success and the resulting file passes checks, making the issue silent and dangerous. The flaw was found during an internal pre-1.0 security review. The fix in 0.18.0 aligns line break handling and rejects files with ambiguous line breaks, preventing this issue.

CWE-193Off-by-one Error (opens in a new tab)
Base weakness
A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
Implementation
When copying character arrays or using character manipulation methods, the correct size parameter must be used to account for the null terminator that needs to be added at the end of the array.
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 10 Nov 2026, 17:47 UTC

WeaknessesCWE-193

Technical details

References

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