EUVD-2026-104991
GHSA-vr39-qqr3-x9v4
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessObtain compromised eMudhra intermediate cert
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DeliveryGain man-in-the-middle network position
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ExploitVictim navigates to HTTPS site
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ExecutionPresent fraudulent certificate accepted by client
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ImpactIntercept or alter TLS traffic
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V12 - Secure Communication Certificate validation
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| Exploitation Conditions | Exploitation requires an attacker to already possess one of the compromised eMudhra intermediate certificates AND to occupy a man-in-the-middle position on the victim's network path; the victim must then initiate an HTTPS connection (UI:R). The flaw is further limited to deployments where the OneCRL block list delivered via RemoteSettings is disabled by policy or otherwise unavailable - in default configurations the 17 October 2026 RemoteSettings push already blocks these certificates, so this binary-bundled fix only closes the residual gap for RemoteSettings-disabled clients. It does not permit code execution and yields only partial (Low) confidentiality and integrity impact against intercepted TLS sessions. |
| Impact | Signals are mixed and point to a low-to-moderate, defense-in-depth issue rather than an active emergency. The provided CVSS 3.1 vector (AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N, base 5.4) describes a network, unauthenticated, user-interaction-dependent flaw with only Low confidentiality and Low integrity impact and no availability impact - consistent with CWE-295 (improper certificate validation). No EPSS score, no CISA KEV listing, and no POC were supplied, so by the precision rules this is 'no public exploit identified at time of analysis.' Importantly, the underlying trigger - compromised intermediate eMudhra certificates - was already revoked by Mozilla via OneCRL/RemoteSettings on 17 October 2026; this CVE/fix merely bundles that blocklist directly into the browser binary so clients are still protected when RemoteSettings is disabled by policy or unreachable. Real-world risk is therefore conditional and narrow: it only matters for users whose RemoteSettings channel was disabled/blocked AND who face an attacker already possessing the compromised certificates in a man-in-the-middle position. The CVSS AC:L arguably understates difficulty, since successful attack requires both an interception position and possession of specific compromised certs - verify against vendor framing. |
| Exploit ScenarioDerived | An attacker who has obtained one of the compromised eMudhra intermediate certificates positions themselves as a man-in-the-middle (e.g., hostile Wi-Fi or network tap) against a Firefox user whose RemoteSettings/OneCRL updates are disabled by enterprise policy or blocked by the network. When the victim browses to an HTTPS site, Firefox accepts the fraudulently-issued certificate and the attacker intercepts or tampers with the TLS session. No public exploit code was identified at time of analysis. |
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Alert meAnalysisAIv1 – Oct 20, 2026
Firefox clients that cannot refresh Mozilla's OneCRL revocation list over RemoteSettings may continue to trust TLS certificates chained to compromised eMudhra intermediate CAs, allowing an attacker positioned on the network path to intercept HTTPS sessions with limited confidentiality and integrity impact. The issue is resolved in Firefox 158.0.1, Firefox ESR 153.5.1 and Firefox ESR 115.43.1 by bundling the updated block list directly into the binary, so the revocation applies even when RemoteSettings is disabled by policy or unreachable. No public exploit code or confirmed active exploitation was identified, and the independent assessment rates this as a low-to-moderate defense-in-depth gap (AC:H) rather than an emergency: the attacker must already hold a compromised eMudhra intermediate certificate and control the victim's traffic path, while default installations were already protected by the 17 October RemoteSettings push.
RemediationAI
Vendor-released patch: Firefox 158.0.1, Firefox ESR 153.5.1 and Firefox ESR 115.43.1 - upgrade all affected clients to these or later builds, since they embed the updated OneCRL block list and enforce it independently of RemoteSettings availability. Because the vulnerable population is precisely the set of clients that cannot reach RemoteSettings, prioritize updating policy-managed, air-gapped and proxy-restricted fleets where the runtime list refresh is suppressed; the bundled list closes the gap without requiring network access. As an interim control for clients that cannot be updated immediately, re-enable RemoteSettings (or remove the policy that disables it) so the 17 October 2026 block list is fetched - the trade-off is that re-enabling the service may conflict with the hardening rationale that led to the policy and requires outbound access to Mozilla's RemoteSettings endpoints. Administrators can additionally neutralize the exposure at the trust-store level by distributing an enterprise policy or OS-level certificate store change that removes or distrusts the affected eMudhra intermediates; this stops interception via those chains but will break any legitimate internal or third-party services still chaining to them, and it must be paired with removal of the corresponding root entries to be effective. Confirm the applied state by checking the browser's certificate revocation/OneCRL state and the build version rather than relying on network connectivity to the update service, and reference the vendor advisories at https://www.mozilla.org/security/advisories/mfsa2026-111/, https://www.mozilla.org/security/advisories/mfsa2026-112/ and https://www.mozilla.org/security/advisories/mfsa2026-113/ for the exact release mapping. Network monitoring for unexpected certificate chains terminating at eMudhra intermediates provides detection coverage for attempted MITM during the remediation window.
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Technical ContextAI · show details
The root cause class is CWE-295, Improper Certificate Validation, and specifically the freshness and availability of the trust-revocation data Firefox relies on. Mozilla's OneCRL is a signed, aggregated block list of revoked intermediate CA certificates distributed to clients through RemoteSettings; it is not a traditional per-connection CRL or OCSP lookup, so its protective value depends entirely on the client being able to fetch and apply updates. When enterprise policy or a restricted network environment suppresses RemoteSettings, a client can retain trust in an intermediate that Mozilla has already revoked - in this case compromised eMudhra intermediates blocked on 17 October 2026. Because intermediate CA compromise sits at the heart of the PKI chain-building logic (Mozilla's built-in root store plus NSS), any leaf certificate issued under such an intermediate would validate normally on a stale client, letting a man-in-the-middle present a certificate the browser accepts. The fix is architectural rather than code-path oriented: ship the authoritative block list inside the release so trust decisions do not depend on runtime network reachability. The CPE cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* reflects that the affected surface is the browser's certificate verification stack across desktop and other Firefox builds prior to the fixed versions; because exploitation requires holding a CA private key and occupying a MITM position, the assessed severity uses AC:H rather than the AC:L in the published base score.
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Severity by source
AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Network attacker needs a MITM position plus possession of specific compromised certificates (AC:H) and victim navigation (UI:R); partial TLS interception yields C:L/I:L, no availability impact.
Primary rating from Vendor (mozilla).
CVSS VectorVendor: mozilla
Lifecycle Timeline
3DescriptionCVE.org
Mozilla blocked compromised intermediate eMudhra certificates via OneCRL on the 17th of October which was distributed to clients via RemoteSettings the same day. This update contains the updated OneCRL block list, ensuring clients will block the compromised certificates even if RemoteSettings is disabled by policy or otherwise unavailable in the user's network environment. This vulnerability was fixed in Firefox 158.0.1, Firefox ESR 153.5.1, and Firefox ESR 115.43.1.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
VulDB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.
Affected Products (CPE)CVE.org
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Exploit-DB