CVE-2026-119284

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.6, joserfc compact JWS deserialization calls bytes.split() before enforcing the existing aggregate segment-size limits. When attacker-controlled compact serialization bytes reach deserialize_compact(), the split creates copies of the header, payload, and signature segments before ExceededSizeError rejects them, causing an additional allocation approximately proportional to the supplied token. Requests that exhaust available process memory can therefore cause an availability failure even though signature verification fails. This issue is fixed in version 1.7.6.

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.6, joserfc compact JWS deserialization calls bytes.split() before enforcing the existing aggregate segment-size limits. When attacker-controlled compact serialization bytes reach deserialize_compact(), the split creates copies of the header, payload, and signature segments before ExceededSizeError rejects them, causing an additional allocation approximately proportional to the supplied token. Requests that exhaust available process memory can therefore cause an availability failure even though signature verification fails. This issue is fixed in version 1.7.6.

Summary

joserfc 1.7.4 defines compact-JWS header, payload, and signature limits, but calls value.split(b".") before validating them. Python bytes.split() copies the attacker-controlled segments, so the current guard allocates roughly one complete payload before rejecting it.

Reproduction

.venv-research/bin/python 06-practical-testing/preauth-memory-profile.py

The input is resident before a fork-isolated verifier runs, and every signature is invalid.

| Input | Peak RSS delta | Amplification | Result | |---:|---:|---:|---| | 1 MiB | 1.11 MiB | 1.11× | size rejected | | 4 MiB | 4.04 MiB | 1.01× | size rejected | | 8 MiB | 8.04 MiB | 1.01× | size rejected | | 16 MiB | 16.04 MiB | 1.00× | size rejected | | 32 MiB | 31.74 MiB | 0.99× | size rejected | | 64 MiB | 63.80 MiB | 1.00× | size rejected |

The unconstrained profile is the primary evidence: joserfc allocates an additional attacker-sized object before producing its intended ExceededSizeError. A separate baseline-plus-headroom stress test raises MemoryError when that copy cannot fit, but this report does not characterize an absolute RLIMIT_AS value as a realistic worker memory budget.

Security Argument

The issue is not that joserfc can prevent the transport layer from receiving a large header. The issue is narrower: once bytes reach deserialize_compact(), the library's existing size guard cannot fulfill its allocation-limiting purpose because attacker-controlled segment copies are created first.

This differs from GHSA-frfh-8v73-gjg4, which concerned embedding already-loaded oversized segments in exception and log messages. Here, the current implementation itself creates an additional payload-sized allocation before its fixed size exception.

Recommended Fix

Check len(value) against a maximum compact-serialization size before split(). If per-segment diagnostics are needed, locate delimiters with bounded find() operations or memory views, validate offsets and lengths, and only then materialize acceptable segments.

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.6, joserfc compact JWS deserialization calls bytes.split() before enforcing the existing aggregate segment-size limits. When attacker-controlled compact serialization bytes reach deserialize_compact(), the split creates copies of the header, payload, and signature segments before ExceededSizeError rejects them, causing an additional allocation approximately proportional to the supplied token. Requests that exhaust available process memory can therefore cause an availability failure even though signature verification fails. This issue is fixed in version 1.7.6.

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.6, joserfc compact JWS deserialization calls bytes.split() before enforcing the existing aggregate segment-size limits. When attacker-controlled compact serialization bytes reach deserialize_compact(), the split creates copies of the header, payload, and signature segments before ExceededSizeError rejects them, causing an additional allocation approximately proportional to the supplied token. Requests that exhaust available process memory can therefore cause an availability failure even though signature verification fails. This issue is fixed in version 1.7.6.

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.6, joserfc compact JWS deserialization calls bytes.split() before enforcing the existing aggregate segment-size limits. When attacker-controlled compact serialization bytes reach deserialize_compact(), the split creates copies of the header, payload, and signature segments before ExceededSizeError rejects them, causing an additional allocation approximately proportional to the supplied token. Requests that exhaust available process memory can therefore cause an availability failure even though signature verification fails. This issue is fixed in version 1.7.6.

Summary

joserfc 1.7.4 defines compact-JWS header, payload, and signature limits, but calls value.split(b".") before validating them. Python bytes.split() copies the attacker-controlled segments, so the current guard allocates roughly one complete payload before rejecting it.

Reproduction

.venv-research/bin/python 06-practical-testing/preauth-memory-profile.py

The input is resident before a fork-isolated verifier runs, and every signature is invalid.

| Input | Peak RSS delta | Amplification | Result | |---:|---:|---:|---| | 1 MiB | 1.11 MiB | 1.11× | size rejected | | 4 MiB | 4.04 MiB | 1.01× | size rejected | | 8 MiB | 8.04 MiB | 1.01× | size rejected | | 16 MiB | 16.04 MiB | 1.00× | size rejected | | 32 MiB | 31.74 MiB | 0.99× | size rejected | | 64 MiB | 63.80 MiB | 1.00× | size rejected |

The unconstrained profile is the primary evidence: joserfc allocates an additional attacker-sized object before producing its intended ExceededSizeError. A separate baseline-plus-headroom stress test raises MemoryError when that copy cannot fit, but this report does not characterize an absolute RLIMIT_AS value as a realistic worker memory budget.

Security Argument

The issue is not that joserfc can prevent the transport layer from receiving a large header. The issue is narrower: once bytes reach deserialize_compact(), the library's existing size guard cannot fulfill its allocation-limiting purpose because attacker-controlled segment copies are created first.

This differs from GHSA-frfh-8v73-gjg4, which concerned embedding already-loaded oversized segments in exception and log messages. Here, the current implementation itself creates an additional payload-sized allocation before its fixed size exception.

Recommended Fix

Check len(value) against a maximum compact-serialization size before split(). If per-segment diagnostics are needed, locate delimiters with bounded find() operations or memory views, validate offsets and lengths, and only then materialize acceptable segments.

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.6, joserfc compact JWS deserialization calls bytes.split() before enforcing the existing aggregate segment-size limits. When attacker-controlled compact serialization bytes reach deserialize_compact(), the split creates copies of the header, payload, and signature segments before ExceededSizeError rejects them, causing an additional allocation approximately proportional to the supplied token. Requests that exhaust available process memory can therefore cause an availability failure even though signature verification fails. This issue is fixed in version 1.7.6.