CVE-2023-25725
Haproxy ≤ 2.0.31
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2023-25725 is a critical-severity HTTP Request/Response Smuggling (CWE-444) vulnerability in Haproxy Haproxy. Its CVSS base score is 9.1 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique LSASS Memory (T1003.001); ranked in the top 7% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
HAProxy versions prior to 2.7.3 are affected by a request smuggling vulnerability that stems from the HTTP/1 header parser accepting empty header field names. This behavior can truncate the list of headers during parsing and processing for HTTP/1.0 and HTTP/1.1 requests, causing selected headers to be lost after initial handling. The same root cause produces more limited effects under HTTP/2 and HTTP/3 because the headers are dropped before they reach the processing stage. Fixed releases are listed as 2.7.3, 2.6.9, 2.5.12, 2.4.22, 2.2.29, and 2.0.31.
An unauthenticated network attacker can craft requests containing empty header names to strip subsequent headers, thereby bypassing access-control checks or other header-dependent policies enforced by HAProxy. The resulting integrity and availability impact is rated high under CVSS 9.1, reflecting the potential for unauthorized actions or service disruption without requiring user interaction.
Advisories from Debian and Fedora, along with the upstream commit, direct users to apply the listed patched versions. The references also include distribution-specific announcements that document the coordinated rollout of these updates.
EPSS for the CVE rose from lower values to a peak of 0.2994 before receding to the current 0.1754, indicating a period of increased exploitation interest after disclosure. No confirmed in-the-wild campaigns are described in the supplied references.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2023-29633
Vulnerability Data
HAProxy before 2.7.3 may allow a bypass of access control because HTTP/1 headers are inadvertently lost in some situations, aka "request smuggling." The HTTP header parsers in HAProxy may accept empty header field names, which could be used to truncate…
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the list of HTTP headers and thus make some headers disappear after being parsed and processed for HTTP/1.0 and HTTP/1.1. For HTTP/2 and HTTP/3, the impact is limited because the headers disappear before being parsed and processed, as if they had not been sent by the client. The fixed versions are 2.7.3, 2.6.9, 2.5.12, 2.4.22, 2.2.29, and 2.0.31.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V4.1.3V4.2.4V1.5.3V4.1.1
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.
Network monitoring can detect smuggling attempts via anomalous HTTP traffic or logs, while eliminating the inconsistency directly aids detection of such events.
Network protections can enforce consistent HTTP proxy/firewall behavior to block smuggling, and removing the weakness helps prevent unauthorized access via request smuggling.
Configuration management can enforce uniform HTTP parsing rules across intermediaries, directly mitigating inconsistent interpretation.
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.