CVE-2026-25899
Published: 24 February 2026
Summary
CVE-2026-25899 is a high-severity Memory Allocation with Excessive Size Value (CWE-789) vulnerability in Gofiber Fiber. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked at the 32.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
This control implements explicit throttling on session allocation, addressing the weakness of allocating resources without limits.
Plan testing exercises resource allocation limits and throttling during simulated failures, directly addressing weaknesses that allow unbounded resource use.
Contingency plan updates ensure recovery strategies address unbounded resource allocation, making it harder for attackers to exploit lack of throttling to cause prolonged outages.
Provides continuity when unbounded resource allocation at the primary site leads to exhaustion and downtime.
Alternate services allow operations to continue when primary allocation of resources lacks limits or throttling.
Explicit planning of security-related actions requires defining limits, windows, and resource allocations, making allocation without throttling far less likely.
Measures of performance include tracking allocation behavior and throttling effectiveness, reducing the window for resource exhaustion attacks.
Imposes an inactivity-based limit on network resource allocation, throttling the number of concurrently held connections.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Unvalidated cookie deserialization in public-facing Go web framework enables direct memory exhaustion DoS via crafted HTTP request, matching application exploitation for endpoint availability impact.
NVD Description
Fiber is an Express inspired web framework written in Go. In versions on the v3 branch prior to 3.1.0, the use of the `fiber_flash` cookie can force an unbounded allocation on any server. A crafted 10-character cookie value triggers an…
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attempt to allocate up to 85GB of memory via unvalidated msgpack deserialization. No authentication is required. Every GoFiber v3 endpoint is affected regardless of whether the application uses flash messages. Version 3.1.0 fixes the issue.
Deeper analysisAI
CVE-2026-25899 affects Fiber, an Express-inspired web framework written in Go, specifically versions on the v3 branch prior to 3.1.0. The vulnerability stems from the `fiber_flash` cookie, which triggers an unbounded memory allocation due to unvalidated msgpack deserialization. A crafted 10-character cookie value can force the server to attempt allocating up to 85GB of memory. Every endpoint in GoFiber v3 applications is vulnerable, regardless of whether the application uses flash messages.
Any unauthenticated attacker with network access can exploit this vulnerability by sending a malicious `fiber_flash` cookie in an HTTP request. This leads to memory exhaustion, enabling a denial-of-service attack that may crash the server or severely degrade performance. The CVSS v3.1 base score is 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), highlighting high availability impact, with associated CWEs-789 (Uncontrolled Memory Allocation) and CWE-770 (Allocation of Resources Without Limits or Throttling).
The Fiber project fixed this issue in version 3.1.0. Mitigation requires upgrading to v3.1.0 or later. Additional details are available in the release notes at https://github.com/gofiber/fiber/releases/tag/v3.1.0 and the security advisory at https://github.com/gofiber/fiber/security/advisories/GHSA-2mr3-m5q5-wgp6.
Details
- CWE(s)