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CVE-2026-107843

MEDIUM 5.3

Published 2026-10-09 · Last modified 2026-10-13

Contao is an Open Source CMS. From version 4.1.0 until 5.3.50 and 5.7.12, ModuleRegistration::compile() enters its follow-up registration branch on any POST to a page containing the registration module without verifying FORM_SUBMIT or the preceding captcha result. resendActivationMail() can then invoke OptInToken::send() without rate limiting, allowing an unauthenticated attacker to cause repeated activation emails to be sent to an address with a pending registration and to determine whether that pending registration exists. The branch is reachable only when reg_activate is enabled and the target has an unconfirmed registration and opt-in token. This issue is fixed in versions 5.3.50 and 5.7.12.

NO EXPLOITATION SIGNALS

No known exploitation, public exploit, or elevated probability at this time. Track for changes.

Exploitation likelihood

0.3%chance of exploitation in 30 days · 19th percentile

○ In CISA KEV ○ Catalogued PoC

Impact if exploited

5.3CVSS 3.1 · MEDIUM

  • ConfidentialityLow
  • IntegrityNone
  • AvailabilityNone

What an attacker needs

  • ✓Access: Reachable over the network — no local access needed
  • ✓Privileges: No account or privileges required
  • ✓User interaction: No user interaction needed
  • ✓Complexity: No special conditions — reliably repeatable

✓ lowers the bar for an attacker · ⚠ raises it

Proof of concept

No public PoC is currently catalogued.

Search for new PoCs

Search GitHub now — results may be empty or unverified.

Tracked sources are checked daily for recent CVEs, including PoCs published after the original disclosure. A later release appears after a tracked source lists it and a refresh succeeds.

Data snapshot:

Affected

Vendors Contao

Products Contao

Weakness (CWE)

  • CWE-204: : Observable Response Discrepancy
  • CWE-770: : Allocation of Resources Without Limits or Throttling

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

References and research data (JSON)

Packages and version ranges

Each advisory describes its own package and affected ranges. A boundary applies to that range; it is not a universal upgrade recommendation.

  • contao/core-bundle Packagist

    pkg:composer/contao/core-bundle

    ECOSYSTEM range
    • Introduced version (included): 4.1.0
    • Fixed boundary (excluded): 5.3.50
    390 explicitly listed affected versions

    4.1.0, 4.1.1, 4.1.2, 4.1.3, 4.10.0, 4.10.0-RC1, 4.10.0-RC2, 4.10.0-RC3, 4.10.0-RC4, 4.10.1, 4.10.2, 4.10.3, 4.10.4, 4.10.5, 4.10.6, 4.10.7, 4.11.0, 4.11.0-RC1, 4.11.0-RC2, 4.11.1, 4.11.2, 4.11.3, 4.11.4, 4.11.5, 4.11.6, 4.11.7, 4.11.8, 4.11.9, 4.12.0, 4.12.0-RC1, 4.12.0-RC2, 4.12.0-RC3, 4.12.1, 4.12.2, 4.12.3, 4.12.4, 4.12.5, 4.12.6, 4.12.7, 4.13.0, 4.13.0-RC1, 4.13.0-RC2, 4.13.0-RC3, 4.13.1, 4.13.10, 4.13.11, 4.13.12, 4.13.13, 4.13.14, 4.13.15, 4.13.16, 4.13.17, 4.13.18, 4.13.19, 4.13.2, 4.13.20, 4.13.21, 4.13.22, 4.13.23, 4.13.24, 4.13.25, 4.13.26, 4.13.27, 4.13.28, 4.13.29, 4.13.3, 4.13.30, 4.13.31, 4.13.32, 4.13.33, 4.13.34, 4.13.35, 4.13.36, 4.13.37, 4.13.38, 4.13.39, 4.13.4, 4.13.40, 4.13.41, 4.13.42, 4.13.43, 4.13.44, 4.13.45, 4.13.46, 4.13.47, 4.13.48, 4.13.49, 4.13.5, 4.13.50, 4.13.51, 4.13.52, 4.13.53, 4.13.54, 4.13.55, 4.13.56, 4.13.57, 4.13.58, 4.13.6, 4.13.7, 4.13.8, 4.13.9, 4.2.0, 4.2.0-RC1, 4.2.0-beta1, 4.2.1, 4.2.2, 4.2.3, 4.2.4, 4.2.5, 4.3.0, 4.3.0-RC1, 4.3.1, 4.3.10, 4.3.11, 4.3.2, 4.3.3, 4.3.4, 4.3.5, 4.3.6, 4.3.7, 4.3.8, 4.3.9, 4.4.0, 4.4.0-RC1, 4.4.0-RC2, 4.4.0-beta1, 4.4.1, 4.4.10, 4.4.11, 4.4.12, 4.4.13, 4.4.14, 4.4.15, 4.4.16, 4.4.17, 4.4.18, 4.4.19, 4.4.2, 4.4.20, 4.4.21, 4.4.22, 4.4.23, 4.4.24, 4.4.25, 4.4.26, 4.4.27, 4.4.28, 4.4.29, 4.4.3, 4.4.30, 4.4.31, 4.4.32, 4.4.33, 4.4.34, 4.4.35, 4.4.36, 4.4.37, 4.4.38, 4.4.39, 4.4.4, 4.4.40, 4.4.41, 4.4.42, 4.4.43, 4.4.44, 4.4.45, 4.4.46, 4.4.47, 4.4.48, 4.4.49, 4.4.5, 4.4.50, 4.4.51, 4.4.52, 4.4.53, 4.4.54, 4.4.55, 4.4.56, 4.4.57, 4.4.6, 4.4.7, 4.4.8, 4.4.9, 4.5.0, 4.5.0-RC1, 4.5.0-RC2, 4.5.0-beta1, 4.5.0-beta2, 4.5.0-beta3, 4.5.1, 4.5.10, 4.5.11, 4.5.12, 4.5.13, 4.5.14, 4.5.2, 4.5.3, 4.5.4, 4.5.5, 4.5.6, 4.5.7, 4.5.8, 4.5.9, 4.6.0, 4.6.0-RC1, 4.6.0-RC2, 4.6.0-RC3, 4.6.1, 4.6.10, 4.6.11, 4.6.12, 4.6.13, 4.6.14, 4.6.2, 4.6.3, 4.6.4, 4.6.5, 4.6.6, 4.6.7, 4.6.8, 4.6.9, 4.7.0, 4.7.0-RC1, 4.7.0-RC2, 4.7.0-RC3, 4.7.0-RC4, 4.7.1, 4.7.2, 4.7.3, 4.7.4, 4.7.5, 4.7.6, 4.7.7, 4.8.0, 4.8.0-RC1, 4.8.0-RC2, 4.8.1, 4.8.2, 4.8.3, 4.8.4, 4.8.5, 4.8.6, 4.8.7, 4.8.8, 4.9.0, 4.9.0-RC1, 4.9.0-RC2, 4.9.1, 4.9.10, 4.9.11, 4.9.12, 4.9.13, 4.9.14, 4.9.15, 4.9.16, 4.9.17, 4.9.18, 4.9.19, 4.9.2, 4.9.20, 4.9.21, 4.9.22, 4.9.23, 4.9.24, 4.9.25, 4.9.26, 4.9.27, 4.9.28, 4.9.29, 4.9.3, 4.9.30, 4.9.31, 4.9.32, 4.9.33, 4.9.34, 4.9.35, 4.9.36, 4.9.37, 4.9.38, 4.9.39, 4.9.4, 4.9.40, 4.9.41, 4.9.42, 4.9.5, 4.9.6, 4.9.7, 4.9.8, 4.9.9, 5.0.0, 5.0.0-RC1, 5.0.0-RC2, 5.0.0-RC3, 5.0.0-RC4, 5.0.1, 5.0.10, 5.0.2, 5.0.3, 5.0.4, 5.0.5, 5.0.6, 5.0.7, 5.0.8, 5.0.9, 5.1.0, 5.1.0-RC1, 5.1.0-RC2, 5.1.0-RC3, 5.1.1, 5.1.10, 5.1.11, 5.1.2, 5.1.3, 5.1.4, 5.1.5, 5.1.6, 5.1.7, 5.1.8, 5.1.9, 5.2.0, 5.2.0-RC1, 5.2.0-RC2, 5.2.0-RC3, 5.2.0-RC4, 5.2.0-RC5, 5.2.0-RC6, 5.2.1, 5.2.10, 5.2.2, 5.2.3, 5.2.4, 5.2.5, 5.2.6, 5.2.7, 5.2.8, 5.2.9, 5.3.0, 5.3.0-RC1, 5.3.0-RC2, 5.3.0-RC3, 5.3.0-RC4, 5.3.1, 5.3.10, 5.3.11, 5.3.12, 5.3.13, 5.3.14, 5.3.15, 5.3.16, 5.3.17, 5.3.18, 5.3.19, 5.3.2, 5.3.20, 5.3.21, 5.3.22, 5.3.23, 5.3.24, 5.3.25, 5.3.26, 5.3.27, 5.3.28, 5.3.29, 5.3.3, 5.3.30, 5.3.31, 5.3.32, 5.3.33, 5.3.34, 5.3.35, 5.3.36, 5.3.37, 5.3.38, 5.3.39, 5.3.4, 5.3.40, 5.3.41, 5.3.42, 5.3.43, 5.3.44, 5.3.45, 5.3.46, 5.3.47, 5.3.48, 5.3.49, 5.3.5, 5.3.6, 5.3.7, 5.3.8, 5.3.9

    Additional upstream package constraints
    {
  "database": {
    "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-mfxh-vp55-7gc6/GHSA-mfxh-vp55-7gc6.json"
  }
}
    GitHub Advisory Database · GHSA-mfxh-vp55-7gc6 · Updated 2026-10-09T21:00:10.232779369Z
  • contao/core-bundle Packagist

    pkg:composer/contao/core-bundle

    ECOSYSTEM range
    • Introduced version (included): 5.4.0-RC1
    • Fixed boundary (excluded): 5.7.12
    71 explicitly listed affected versions

    5.4.0, 5.4.0-RC1, 5.4.0-RC2, 5.4.0-RC3, 5.4.0-RC4, 5.4.1, 5.4.10, 5.4.11, 5.4.12, 5.4.13, 5.4.14, 5.4.2, 5.4.3, 5.4.4, 5.4.5, 5.4.6, 5.4.7, 5.4.8, 5.4.9, 5.5.0, 5.5.0-RC1, 5.5.0-RC2, 5.5.0-RC3, 5.5.0-RC4, 5.5.1, 5.5.10, 5.5.11, 5.5.12, 5.5.13, 5.5.14, 5.5.15, 5.5.16, 5.5.2, 5.5.3, 5.5.4, 5.5.5, 5.5.6, 5.5.7, 5.5.8, 5.5.9, 5.6.0, 5.6.0-RC1, 5.6.0-RC2, 5.6.0-RC3, 5.6.1, 5.6.10, 5.6.11, 5.6.2, 5.6.3, 5.6.4, 5.6.5, 5.6.6, 5.6.7, 5.6.8, 5.6.9, 5.7.0, 5.7.0-RC1, 5.7.0-RC2, 5.7.0-RC3, 5.7.0-RC4, 5.7.1, 5.7.10, 5.7.11, 5.7.2, 5.7.3, 5.7.4, 5.7.5, 5.7.6, 5.7.7, 5.7.8, 5.7.9

    Additional upstream package constraints
    {
  "database": {
    "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-mfxh-vp55-7gc6/GHSA-mfxh-vp55-7gc6.json"
  }
}
    GitHub Advisory Database · GHSA-mfxh-vp55-7gc6 · Updated 2026-10-09T21:00:10.232779369Z

All CVSS metrics

  • MEDIUM 5.3 v3.1 · CNA Primary
    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
  • MEDIUM 5.3 v3.1 · NVD Secondary
    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

References

Advisories

Technical & other

Sources: NVD · CVE.org · EPSS