2.3

CVE-2026-62995: joserfc accepts JWT with padding, leading to JWT malleability

Deferred
AliasesUBUNTU-CVE-2026-62995DEBIAN-CVE-2026-62995openSUSE-SU-2026:11423-1
Published 29-07-2026Last modified 30-07-2026

Vulnerability summary

CVE-2026-62995 is a low (CVSS 2.3) vulnerability in authlib joserfc. EPSS estimates a 0.14% chance of exploitation in the next 30 days, higher than 3.7% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 2.3, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
2.3/10
010
Low · v4.0 (CVE.org)
EPSS score
0.14%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 1
RHSA-2026:48758

Timeline

  1. 29-07-2026
    PublishedVulnerability first disclosed.
  2. 30-07-2026
    Last modifiedVulnerability information updated.

Description

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. in versions 1.7.1 and prior, joserfc accepts JWTs with trailing padding (==) which are not conforming to the JOSE specifications. This leads to malleability of the JWTs when consumed by joserfc. Depending on this application this might or not be an issue. This could lead to bypass of token revocation or anti-replay protection when implemented as a deny list of tokens or a deny list of token hashes. Note that ECDSA JWS are always malleable because of the malleability of ECDSA signatures (first test case in the code bellow). This makes a scheme which assumes that JWTs are not malleable brittle. However for other signatures (or MAC) schemes it might make sense to assume non malleability of the token. This issue has been fixed in version 1.7.2.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.14%

Chance of exploitation in the next 30 days

Percentile

4%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.14% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Opensuse2 products
  • python-joserfc&distro=openSUSE Leap 16.0< 1.1.0-bp160.4.1
  • python-joserfc&distro=openSUSE Tumbleweed< 1.7.4-2.1
Authlib1 product
Debian1 product
  • joserfcAll versions (No fix recorded) | < 1.7.2-1
Ubuntu1 product
  • joserfcAll versions (No fix recorded)

4 vendors · 5 products

References

6 links