VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2025-61920: Safety · Authlib is vulnerable to Denial of Service via Oversized JOSE Segments

Affects safetySource GCVE Database

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Not known to be exploited · CVSS 7.5 High : upgrade to 3.6.2_1 soon.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

7.5High

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

Patch: Available – fixed in 3.6.2_1

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

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

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: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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

Upgrade safety to 3.6.2_1.

Affected software

Product	Affected	Fixed in
Homebrewsafety`pkg:brew/safety`Other threats	Affected >=3.2.4 <3.6.2_1	Fixed in 3.6.2_1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

**Summary** Authlib’s JOSE implementation accepts unbounded JWS/JWT header and signature segments. A remote attacker can craft a token whose base64url‑encoded header or signature spans hundreds of megabytes. During verification, Authlib decodes and parses the full input before it is rejected, driving CPU and memory consumption to hostile levels and enabling denial of service. **Impact** - Attack vector: unauthenticated network attacker submits a malicious JWS/JWT. - Effect: base64 decode + JSON/crypto processing of huge buffers pegs CPU and allocates large amounts of RAM; a single request can exhaust service capacity. - Observed behaviour: on a test host, the legacy code verified a 500 MB header, consuming ~4 GB RSS and ~9 s CPU before failing. - Severity: High. CVSS v3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (7.5). Affected Versions Authlib ≤ 1.6.3 (and earlier) when verifying JWS/JWT tokens. Later snapshots with 256 KB header/signature limits are not affected. **Proof of concept** Local demo (do not run against third-party systems): Download [jws_segment_dos_demo.py](https://github.com/user-attachments/files/22450820/jws_segment_dos_demo.py) the PoC in direcotry authlib/ Run following Command ``` python3 jws_segment_dos_demo.py --variant both --sizes "500MB" --fork-per-case ``` Environment: Python 3.13.6, Authlib 1.6.4, Linux x86_64, CPUs=8 Sample output: Refined <img width="1295" height="306" alt="image" src="https://github.com/user-attachments/assets/6dd8410f-bc36-4717-8cee-649bac9bf291" /> The compilation script prints separate “[ATTACKER]” (token construction) and “[SERVER]” (Authlib verification) RSS deltas so defenders can distinguish client-side preparation from server-side amplification. Regression tests authlib/tests/dos/test_jose_dos.py further capture the issue; the saved original_util.py/original_jws.py reproductions still accept the malicious payload. **Remediation** - Apply the upstream patch that introduces decoded size limits: - MAX_HEADER_SEGMENT_BYTES = 256 KB - MAX_SIGNATURE_SEGMENT_BYTES = 256 KB - Enforce Limits in authlib/jose/util.extract_segment and _extract_signature. - Deploy the patched release immediately. - For additional defence in depth, reject JWS/JWT inputs above a few kilobytes at the proxy or WAF layer, and rate-limit verification endpoints. **Workarounds (temporary)** - Enforce input size limits before handing tokens to Authlib. - Use application-level throttling to reduce amplification risk. **Resources** - Demo script: jws_segment_dos_demo.py - Tests: authlib/tests/dos/test_jose_dos.py - OWASP JWT Cheat Sheet (DoS guidance)

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