VulnerabilityPublished 2 Dec 2025

CVE-2025-55181: Facebook proxygen · Excessive Iteration

Affects Facebook proxygenSource CVE Database V5

Not known to be exploited · CVSS 5.3 Medium.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 21% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
GitHubfacebook/proxygen`pkg:github/facebook/proxygen`Other threats	Affected =2025.08.25.00	Fixed in–

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AI-suggested

To mitigate CVE-2025-55181, European organizations should implement strict limits on HTTP request and response body sizes at the network perimeter or within proxygen configurations if possible. Deploying web application firewalls (WAFs) or reverse proxies that enforce maximum payload sizes can prevent excessively large requests from reaching vulnerable components. Monitoring and alerting on abnormal HTTP payload sizes and unusual memory consumption patterns in proxygen processes can provide early detection of exploitation attempts. Isolating proxygen instances in containerized or sandboxed environments limits the blast radius of potential crashes. Organizations should also track updates from Facebook/Meta for patches addressing this vulnerability and plan prompt deployment once available. Reviewing and hardening QUIC and HTTP/2 traffic handling configurations can reduce exposure. Finally, conducting regular stress testing and resilience assessments helps ensure systems can handle edge cases without failure.

Description

Sending an HTTP request/response body with greater than 2^31 bytes triggers an infinite loop in proxygen::coro::HTTPQuicCoroSession which blocks the backing event loop and unconditionally appends data to a std::vector per-loop iteration. This issue leads to unbounded memory growth and eventually causes the process to run out of memory.

Impact

For European organizations, the primary impact of CVE-2025-55181 is a denial of service condition affecting services relying on Facebook's proxygen library for HTTP/QUIC communication. This can disrupt web services, APIs, or internal communications that use proxygen, potentially causing downtime or degraded performance. Organizations handling large volumes of HTTP traffic or those exposed to untrusted networks are at higher risk. The unbounded memory consumption can lead to server crashes or require costly restarts, impacting business continuity and user experience. While confidentiality and integrity are not directly compromised, availability issues can indirectly affect compliance with service-level agreements (SLAs) and regulatory requirements such as GDPR, especially if critical services become unavailable. Additionally, the vulnerability could be leveraged as part of a broader attack strategy to exhaust resources and distract security teams.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 9 Dec 2025, 22:23 UTC

WeaknessesCWE-834

Technical details

References

Community reviews

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