CERTFR-2026-ALE-015
Vulnerability from certfr_alerte - Published: 2026-11-05 - Updated: 2026-11-05
Le 5 novembre 2026, OpenSSH a publié un avis de sécurité concernant une vulnérabilité qui permet à un attaquant de contourner l’authentification d'un service SSH.
En effet, sur les systèmes Linux qui utilisent la bibliothèque standard C musl, compilés sans support PAM ou avec PAM désactivé, un attaquant peut se connecter en fournissant deux mots de passe, dont le deuxième est d'une longueur strictement supérieure à 256 caractères et inférieure à 1024.
Lorsque les conditions sont réunies, cette vulnérabilité est triviale à exploiter. Il convient donc de vérifier si le système est dans une configuration vulnérable.
Indicateurs de compromission
Le chercheur, qui a découvert la vulnérabilité, recommande de vérifier la légitimité des connexions de chaque compte système avec une étoile (:*:) (mot de passe désactivé) dans /etc/shadow. Par exemple, la commande suivante peut être lancée en root :
awk -F : '$2 == "*" {print $1}' /etc/shadow | xargs -r -I{} grep "Accepted password for {}" /var/log/messages
Mesure de contournement
Il est préférable de désactiver l'authentification par mot de passe ou, à défaut, de désactiver le service, si l'application du correctif est impossible.
Solutions
Se référer au bulletin de sécurité de l'éditeur pour l'obtention des correctifs (cf. section Documentation).
| Title | Publication Time | Tags | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
|||||||||||
{
"$ref": "https://www.cert.ssi.gouv.fr/openapi.json",
"affected_systems": [
{
"description": "OpenSSH versions ant\u00e9rieures \u00e0 10.6p2",
"product": {
"name": "OpenSSH",
"vendor": {
"name": "OpenSSH",
"scada": false
}
}
}
],
"affected_systems_content": "",
"closed_at": null,
"content": "## Solutions\n\nSe r\u00e9f\u00e9rer au bulletin de s\u00e9curit\u00e9 de l\u0027\u00e9diteur pour l\u0027obtention des correctifs (cf. section Documentation).",
"cves": [],
"initial_release_date": "2026-11-05T00:00:00",
"last_revision_date": "2026-11-05T00:00:00",
"links": [
{
"title": "Avis CERT-FR CERTFR-2026-AVI-1468 du 5 novembre 2026",
"url": "/avis/CERTFR-2026-AVI-1468/"
},
{
"title": "sshhole",
"url": "https://sshhole.com/"
}
],
"reference": "CERTFR-2026-ALE-015",
"revisions": [
{
"description": "Version initiale",
"revision_date": "2026-11-05T00:00:00.000000"
}
],
"risks": [
{
"description": "Contournement de la politique de s\u00e9curit\u00e9"
}
],
"summary": "Le 5 novembre 2026, OpenSSH a publi\u00e9 un avis de s\u00e9curit\u00e9 concernant une vuln\u00e9rabilit\u00e9 qui permet \u00e0 un attaquant de contourner l\u2019authentification d\u0027un service SSH.\u003cbr\u003e\nEn effet, sur les syst\u00e8mes Linux qui utilisent la biblioth\u00e8que standard C musl, compil\u00e9s sans support PAM ou avec PAM d\u00e9sactiv\u00e9, un attaquant peut se connecter en fournissant deux mots de passe, dont le deuxi\u00e8me est d\u0027une longueur strictement sup\u00e9rieure \u00e0 256 caract\u00e8res et inf\u00e9rieure \u00e0 1024.\n\nLorsque les conditions sont r\u00e9unies, cette vuln\u00e9rabilit\u00e9 est triviale \u00e0 exploiter. Il convient donc de v\u00e9rifier si le syst\u00e8me est dans une configuration vuln\u00e9rable.\n\n## Indicateurs de compromission\n\nLe chercheur, qui a d\u00e9couvert la vuln\u00e9rabilit\u00e9, recommande de v\u00e9rifier la l\u00e9gitimit\u00e9 des connexions de chaque compte syst\u00e8me avec une \u00e9toile \u003ccode\u003e(:\\*:)\u003c/code\u003e (mot de passe d\u00e9sactiv\u00e9) dans \u003ccode\u003e/etc/shadow\u003c/code\u003e. Par exemple, la commande suivante peut \u00eatre lanc\u00e9e en root :\n\u003ccode\u003eawk -F : \u0027$2 == \"*\" {print $1}\u0027 /etc/shadow | xargs -r -I{} grep \"Accepted password for {}\" /var/log/messages\u003c/code\u003e\n\n\n## Mesure de contournement\n\nIl est pr\u00e9f\u00e9rable de d\u00e9sactiver l\u0027authentification par mot de passe ou, \u00e0 d\u00e9faut, de d\u00e9sactiver le service, si l\u0027application du correctif est impossible.",
"title": "Vuln\u00e9rabilit\u00e9 dans OpenSSH",
"vendor_advisories": [
{
"published_at": "2026-11-05",
"title": "Bulletin de s\u00e9curit\u00e9 OpenSSH release-10.6p2",
"url": "https://www.openssh.org/txt/release-10.6p2"
}
]
}
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Nomenclature
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