CVE-2026-48525VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

hermes-agent · PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS

Affects hermes-agentSource GCVE Database

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Authoritative record:CVE-2026-48525· Medium 5.3

Not known to be exploited · CVSS 5.3 Medium : upgrade to 2026.7.1 when convenient.

Data as of 30 Oct 2026, 09:02 UTC

CVSS 3.1 base score

5.3Medium

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

Patch: Available – fixed in 2026.7.1

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 28 May 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 hermes-agent to 2026.7.1.

Affected software

Product	Affected	Fixed in
Homebrewhermes-agent`pkg:brew/hermes-agent`Other threats	Affected >=2026.4.30 <2026.7.1	Fixed in 2026.7.1

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

AI-suggested

A patch is available in PyJWT version 2.12.1 and later that fixes this issue by reordering the decode logic to avoid unnecessary Base64URL decoding of the unused payload segment when 'b64' is false. Users should upgrade to version 2.12.1 or later to remediate this vulnerability. If upgrading immediately is not possible, enforcing strict request body size limits upstream (e.g., in proxies or web servers) can help mitigate the amplification effect by bounding the maximum payload size accepted.

Description

PyJWT versions from 2.4.0 up to but not including 2.12.1 contain a vulnerability in the handling of detached JWS tokens with the unencoded-payload option (b64=false). The library performs Base64URL decoding of the payload segment before enforcing detached payload rules, causing unnecessary CPU and memory usage even if the signature is invalid. This allows an unauthenticated remote attacker to cause a denial of service (DoS) by sending tokens with large payload segments, amplifying resource consumption on the server.

Impact

An unauthenticated remote attacker can exploit this vulnerability to cause a denial of service by sending JWS tokens with large Base64URL-encoded payload segments. The decoding step consumes CPU and memory resources linearly proportional to the payload size, potentially leading to request queueing and worker starvation under modest concurrency. The signature verification occurs after the expensive decode step, so the attacker does not need a valid signing key. This can disrupt availability of services that verify detached JWS tokens using vulnerable PyJWT versions.

Summary

PyJWT's decode_complete() method first decodes the Base64URL payload segment unconditionally before checking if the 'b64' header parameter is false, which indicates that the payload is detached and should be replaced by the caller-provided detached_payload. This leads to an unnecessary and potentially very expensive Base64URL decoding step of an attacker-controlled payload segment that is discarded afterward. Because this decoding happens prior to signature verification, an attacker can send tokens with very large payload segments to cause CPU and memory exhaustion, resulting in an unauthenticated denial of service against endpoints verifying detached JWS tokens using PyJWT. The vulnerability affects PyJWT versions starting from 2.4.0, when detached payload support was introduced, up to 2.12.1 where it was confirmed and fixed.

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Affected software

Description

AI analysisMachine-generated, updated 30 Oct 2026, 09:02 UTC

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