Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HSummary
CVE-2026-11856 is a critical-severity Authentication Bypass by Capture-replay (CWE-294) vulnerability in Haxx Curl. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Unsecured Credentials (T1552); ranked at the 45th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and SC-8 (Transmission Confidentiality and Integrity) — see the control section below for these in your framework.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-41501
Vulnerability Data
Successfully using libcurl to do a transfer to a specific HTTP origin (`hostA`) with **Digest** authentication and then changing the origin to a different one (`hostB`) for a second transfer, reusing the same handle, makes libcurl wrongly pass on the…
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`Authorization:` header field meant for `hostA`, to `hostB`.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The vulnerability causes unintended leakage of HTTP Digest Authorization headers (credentials) to an incorrect origin when a libcurl handle is reused, directly facilitating credential access via T1552 Unsecured Credentials.
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
Mitigating Controls (NIST 800-53 r5) AI
Enforces cryptographic protection of HTTP transmissions, preventing exposure or misuse of sensitive Authorization headers across different origins.
Enforces information flow policies so that credentials or headers bound to one origin (hostA) cannot be sent to another (hostB).
Validates that security-relevant inputs (e.g., Authorization headers) are appropriate for the current destination before transmission.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Protecting and verifying identity assertions prevents replay of captured authentication material.
Encryption and integrity protections for data-in-transit directly block capture-replay of credentials or tokens.
Network monitoring may detect anomalous replays after the fact but does not prevent the design flaw.
Strong authentication methods can reduce replay risk but do not inherently address captured messages.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Cryptographic protections (e.g., nonces, timestamps, message authentication codes) make captured authentication messages unusable for replay.
Secure authentication mechanisms directly prevent replay attacks by requiring fresh, non-replayable credentials or tokens.
Network security controls such as encryption and integrity protection reduce the feasibility of capturing and replaying authentication traffic.
Application security requirements can mandate replay-resistant authentication designs, but the control itself does not prescribe the technical measures.