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FA-27911 / HTTP redirects / Open access

Validate raw target text before any URL normalization: backslash rejection · case 01

A backslash inside a redirect target reaches a different downstream parser.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The backslash-rejection decision uses "raw.startswith('\\\\')"; this violates the stipulated controller policy.

THE FAILURE

The backslash-rejection decision uses "raw.startswith('\\\\')"; this violates the stipulated controller policy.

Unsuccessful approach: The partial repair uses "raw.endswith('\\\\')" and still fails an explicit boundary or control.

Case contract

Validate raw target text before any URL normalization. The explicit fixture inputs and outputs define a bounded offline policy; request identity must accompany the decision.

Why this case matters

Models a redirect controller decision before following a target or exposing a redirect result.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
from urllib.parse import urlsplit, unquote, quote
import posixpath
import re
N = 1
observations = []
def solve(request, raw):
    return {'request': request, 'decision': ['\r' in raw or '\n' in raw, '\t' in raw.strip(' \t'), '\x00' in raw, bool(re.search(r'%(?![0-9A-Fa-f]{2})', raw)), raw.startswith('\\')]} 
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve('/requests/' + str(N) + '/0', '/a\rb\tc\x00d%G0\\e'), {'request': '/requests/' + str(N) + '/0', 'decision': [True, True, True, True, True]})
check('fixture 2', solve('/requests/' + str(N) + '/1', '\t/a%20b\t'), {'request': '/requests/' + str(N) + '/1', 'decision': [False, False, False, False, False]})
check('fixture 3', solve('/requests/' + str(N) + '/2', '/a\nb'), {'request': '/requests/' + str(N) + '/2', 'decision': [True, False, False, False, False]})
check('fixture 4', solve('/requests/' + str(N) + '/3', '/a%'), {'request': '/requests/' + str(N) + '/3', 'decision': [False, False, False, True, False]})
check('fixture 5', solve('/requests/' + str(N) + '/4', '/normal'), {'request': '/requests/' + str(N) + '/4', 'decision': [False, False, False, False, False]})
check('fixture 6', solve('/requests/' + str(N) + '/5', ''), {'request': '/requests/' + str(N) + '/5', 'decision': [False, False, False, False, False]})
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
fixture 1{'decision': [True, True, True, True, False], 'request': '/requests/1/0'}{'decision': [True, True, True, True, True], 'request': '/requests/1/0'}Failed
fixture 2{'decision': [False, False, False, False, False], 'request': '/requests/1/1'}{'decision': [False, False, False, False, False], 'request': '/requests/1/1'}Passed
fixture 3{'decision': [True, False, False, False, False], 'request': '/requests/1/2'}{'decision': [True, False, False, False, False], 'request': '/requests/1/2'}Passed
fixture 4{'decision': [False, False, False, True, False], 'request': '/requests/1/3'}{'decision': [False, False, False, True, False], 'request': '/requests/1/3'}Passed
fixture 5{'decision': [False, False, False, False, False], 'request': '/requests/1/4'}{'decision': [False, False, False, False, False], 'request': '/requests/1/4'}Passed
fixture 6{'decision': [False, False, False, False, False], 'request': '/requests/1/5'}{'decision': [False, False, False, False, False], 'request': '/requests/1/5'}Passed

SHA-256 / b6bc221d5d247c95427ad397760fe78869bb6b98655375b8253933058d6044ff

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
from urllib.parse import urlsplit, unquote, quote
import posixpath
import re
N = 1
observations = []
def solve(request, raw):
    return {'request': request, 'decision': ['\r' in raw or '\n' in raw, '\t' in raw.strip(' \t'), '\x00' in raw, bool(re.search(r'%(?![0-9A-Fa-f]{2})', raw)), raw.endswith('\\')]} 
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1', solve('/requests/' + str(N) + '/0', '/a\rb\tc\x00d%G0\\e'), {'request': '/requests/' + str(N) + '/0', 'decision': [True, True, True, True, True]})
check('fixture 2', solve('/requests/' + str(N) + '/1', '\t/a%20b\t'), {'request': '/requests/' + str(N) + '/1', 'decision': [False, False, False, False, False]})
check('fixture 3', solve('/requests/' + str(N) + '/2', '/a\nb'), {'request': '/requests/' + str(N) + '/2', 'decision': [True, False, False, False, False]})
check('fixture 4', solve('/requests/' + str(N) + '/3', '/a%'), {'request': '/requests/' + str(N) + '/3', 'decision': [False, False, False, True, False]})
check('fixture 5', solve('/requests/' + str(N) + '/4', '/normal'), {'request': '/requests/' + str(N) + '/4', 'decision': [False, False, False, False, False]})
check('fixture 6', solve('/requests/' + str(N) + '/5', ''), {'request': '/requests/' + str(N) + '/5', 'decision': [False, False, False, False, False]})
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
fixture 1{'decision': [True, True, True, True, False], 'request': '/requests/1/0'}{'decision': [True, True, True, True, True], 'request': '/requests/1/0'}Failed
fixture 2{'decision': [False, False, False, False, False], 'request': '/requests/1/1'}{'decision': [False, False, False, False, False], 'request': '/requests/1/1'}Passed
fixture 3{'decision': [True, False, False, False, False], 'request': '/requests/1/2'}{'decision': [True, False, False, False, False], 'request': '/requests/1/2'}Passed
fixture 4{'decision': [False, False, False, True, False], 'request': '/requests/1/3'}{'decision': [False, False, False, True, False], 'request': '/requests/1/3'}Passed
fixture 5{'decision': [False, False, False, False, False], 'request': '/requests/1/4'}{'decision': [False, False, False, False, False], 'request': '/requests/1/4'}Passed
fixture 6{'decision': [False, False, False, False, False], 'request': '/requests/1/5'}{'decision': [False, False, False, False, False], 'request': '/requests/1/5'}Passed

SHA-256 / b9dbdaf2c6be1debdbec55ed40c02fe0700f823a8e9133e3593627bcc11b3ef3

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 6 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Stipulated offline redirect policy, not a complete HTTP, browser, URL, cache, or security implementation. Numbered variants vary request correlation identity. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:41:29.292785+00:00.

Case digest / bae64296ffccae9e803592ae762fe3218d3eeabe6ddfaf0170f3cffeea9ebeb3